In Book 1 of Cicero’s On the nature of the gods, Velleius argues for an Epicurean theology and view of religion. Cotta, an Academic skeptic, argues against him. I argue that when we see Cicero’s creative hand adapting Epicurean texts like the On Piety found at Herculaneum and attributed to Philodemus, we find that Velleius’ speech may be understood as proceeding from our allegedly natural concept that the gods are eternal and happy. Velleius’ seemingly intemperate criticism of his opponents, that they are crazy, follows from his position that they have somehow gone against this natural concept. His positive view, which proceeds from the happiness or blessedness (beatitudo, beatitas, eudaimonia) of the gods, is that Roman religion may be reinterpreted as worship of gods who do not care about us at all, and thus are ideals for us of the hedonist life free from pain. Despite Cicero’s habitual contempt for Epicureanism, he paints an attractive picture of Velleius’ spirituality. But Cotta argues that by making the gods not care for us, Epicurus has torn out the heart from religion, since he has made gods who are (so Cotta argues) selfish and not worthy of worship or imitation.

Being a radical Academic skeptic, Cicero as author does not endorse an answer to the questions of On the nature of the gods and On divination. But when he portrays himself as a character in the dialogues, he portrays himself as finding plausible on those occasions a consistent philosophical theology and view of religion. I suggest that this is meant to model the free reaction of a skeptical mind to debates on questions where the skeptic forms no beliefs. The view that Cicero portrays as plausible to "himself" is the Stoic theology that the natural world is divine and benevolent, except that he finds implausible the Stoic view that divination delivers information from the gods (although he says that divinatory practices at Rome should continue for other reasons). Taking this attitude would be one way to "moderate" Roman religion, that is, to avoid impiety and superstition in practising it, but the reader is left free to make up his or her own mind.

In Book 2 of Cicero’s On the nature of the gods, Balbus argues for a Stoic theology and view of religion, and in Book 3 Cotta, an Academic skeptic, argues against him. I argue that both characters are supporters of traditional Roman pagan religion. In contrast to the Epicurean Velleius in Book 1, Balbus argues that the gods do care for us, in fact that the cosmic god fates every detail of our lives. He describes a world whose beauty is a principle reason to think that this rational creator has planned it for us, and further argues that this creator is good. He offers a complex rereading of Roman religion and poetic myth, according to which Roman religious practices were begun in ways that Stoic theology can support, and that it can still support once later distortions of this theology have been cleared away. Cotta, a pontifex, says that his skepticism is consistent with his priestly office, on grounds reminiscent of modern fideism. But he argues that Balbus’ dogmatic Stoic theology would destabilize the beliefs of those practising Roman religion, because Balbus cannot rigorously relate the many Roman gods to the one Stoic cosmic god.

This chapter on participation in goodness, and on ethics or a good life, has been prepared for by the previous chapter, on beauty and desire. Like the chapter on truth and epistemology before that, this chapter on goodness is robustly realist: it sees what would be morally good for a person, community, or situation to align with the reality and good of the thing considered, which it has by participation in God. The twin focuses here are virtue ethics (which is explored in terms of the alignment of the good-as-moral with the good-as-excellent) and natural law (which is explored in terms of the alignment of the good-as-moral with the good-as-beneficial). No firm wedge, however, is driven between those two approaches, which are both related to God as source and goal in participatory terms. The chapter moves to a discussion of the expectation of the coherence of the good in a participatory framework, such that the goodness that creatures have (and, here, especially human beings) is expected naturally to align with the nature of the good as communicated, for instance, in revelation. This is explored in contrast with the thought of John Duns Scotus. The chapter ends with a participatory discussion of the nature of law in its various forms, including the participatory and theological backdrop to notions of international law.

The Conclusion explores the theme of relation as integral to any participatory vision, on the basis that if all things come forth from God, then they come forth intrinsically related. Relation, and the joys and duties that accompany it, is not some secondary overlay. Here we pick up the theme of 'intra-finite participation' (the participation in, or reception from, one creature in relation to another) explored in the chapter on truth and epistemology. Central test cases here come up in the notion of the common good, and its place in a theological vision of just economics. The chapter, and the book, end where the book began, with the theme of gift: that every good and perfect gift is 'from above, coming down from the Father of lights', as the Letter of James has it.

In the first of five opening chapters on participation and divine causation, we look at 'efficient' or 'agent' causation: what it means, from a participatory perspective, for God to be the cause and agent of creation. The chapter situates the idea of participation within the foundational doctrine, common to the Abrahamic faiths, of creation as being ex nihilo. Nothing is coaeval with God; nor did God rely upon anything else for creation: on eternally existent matter, for instance. Creation is not some past event, now over, but should rather be seen as a relation of dependence upon the creator. This is explored in terms of gift and of the relation of the doctrine of creation to the doctrine of God. This leads on to a discussion of theological apologetics.

In the writing of Thomas Aquinas, and more widely, the metaphysics of participation goes hand in hand with an account of language set out in terms of analogy (and particularly in relation to religious language). The question of how human words can have the capacity to bear witness to God is acknowledged as a real and considerable problem. The response provided here comes from Aquinas: words that we have learned, in by use in relation to creatures, can have bearing for discussion of God (not least as given in revelation) because the perfections that we name in creatures are first, foundationally, and causally, in God. The approach summed up as 'analogy' is contrasted with two others: equivocity and univocity. An analogical approach to language is seen to be present in the scriptures. The chapter closes with a survey of some of the forms of analogy that were put forth in the High Middle Ages.

Within a participatory framework of metaphysics, evil is characteristically seen as a matter of privation. If all being, characterfulness, and action are had by creatures as a participation in, or from, God, then evil is a failure or occlusion of that participation. In this chapter, evil-as-privation is explored in terms of evil as washed-out, senseless, and always taking a form that is strictly relative to the particular good of the particular creature. The chapter ends with a discussion of the non-concurrence of God in evil, and how it might be that evil is possible. Evil is seen to have the character of non-relation between creatures.

Under the title of 'participation', theologians and philosophers have explored what it means for the reality that we observe, and in which we dwell, to have its origin in a divine or transcendent source. This introductory chapter surveys what is to come in this book on the theme of participation. It considers the principal sources that are to be used, especially the Christian Bible and the writings of Thomas Aquinas. It also considers the relation between philosophy and theology, and between conceptual studies and their application within the practical details of a life lived with an eye to participation.

The final chapters of this book look at how a participatory outlook can inform and has informed a vision of the world and what it means to live, act, pray, and seek God in it. This, the first of these chapters, considers knowledge and knowing in participatory terms. Knowledge is seen as a participation of the knower in the known, or a sharing from the known to the knower. This undergirds a 'realist' epistemology, in that knowing rests on the reality of the thing that is known. That said, it also stresses the creaturehood and particularity of the knower and the manner of knowing: that which is known comes to be in the knower in the manner of the knower, whether we are talking about our knowledge of an animal, of a plant, or of God. In the case of God, most of all, the knower never exhausts the depths of what is known. That also applies, however, although to a different degree, in the knowledge of even mundane things, since their deepest reality is a participation in God, which confers a creaturely form of inexhaustibility. In these ways, much of this chapter is an exploration of 'intra-finite participation': about how one creature participates in, or donates to, another. It closes with a discussion of the relation between reason and revelation.

The first five chapters of the book examine the relation of creation to creator in terms of Aristotle's 'four causes' (or four aspects of causation): that God is the efficient, formal (or exemplar), and final cause of creation, but not the material cause. In this chapter, we consider further what it would mean to describe God as a cause, and relate the three of Aristotle's aspects of causation that can be applied analogically to God to the three Persons of the Trinity. The history of speaking in this way – of 'appropriating' divine acts or aspects of divine acts to Persons of the Trinity – is considered. Also discussed here are ways in which the language of participation has been used to talk about inter-Trinitarian relations.

In this chapter, we take a step back and consider a range of underlying concepts and metaphors that express something of what it means to participate, in or from another, and particularly to participate in or from God. 'Part of' language is found to have little value, while the idea of 'part in' is more promising. Notions of a limited reception from another have also been significant, as has the language of likeness. Two approaches are found to be particularly valuable: the idea of reception from a boundless source according to the distinct mode of being of the recipient, and the relation of source to recipient that is indicated by causation.

In the first of five opening chapters on participation and divine causation, we look at 'efficient' or 'agent' causation: what it means, from a participatory perspective, for God to be the cause and agent of creation. The chapter situates the idea of participation within the foundational doctrine, common to the Abrahamic faiths, of creation as being ex nihilo. Nothing is coaeval with God; nor did God rely upon anything else for creation: on eternally existent matter, for instance. Creation is not some past event, now over, but should rather be seen as a relation of dependence upon the creator. This is explored in terms of gift and of the relation of the doctrine of creation to the doctrine of God. This leads on to a discussion of theological apologetics.

In the third section of the book, a range of topics from doctrinal or systematic theology are considered, building on the survey of the first part of the book, which had dealt mainly with the doctrines of God and of creation. This chapter turns to Christology: to the doctrine of the Person of Christ and of the Incarnation, where participatory language and thinking have also been important. This is worked through in terms of a number of central contentions in traditional Christology. It also brings some less-often-considered aspects of the doctrine of Christ to the surface, such as Christ's participation in God through growth in virtues. A participatory account of Christology can bear witness to the full revelation and presence of God in, and as, Christ. This is contrasted with kenotic Christology.

In the third section of the book, a range of topics from doctrinal or systematic theology are considered, building on the survey of the first part of the book, which had dealt mainly with the doctrines of God and of creation. This chapter turns to Christology: to the doctrine of the Person of Christ and of the Incarnation, where participatory language and thinking have also been important. This is worked through in terms of a number of central contentions in traditional Christology. It also brings some less-often-considered aspects of the doctrine of Christ to the surface, such as Christ's participation in God through growth in virtues. A participatory account of Christology can bear witness to the full revelation and presence of God in, and as, Christ. This is contrasted with kenotic Christology.

Ideas of likeness are central to accounts of participation. In this chapter, we consider not only what it means for creatures to derive their existence (or – better – being) from God but also their nature, essence, or characterfulness. This is the territory of exemplarity and exemplary causation. A Platonic tradition of thinking about exemplarity is considered, not least in terms of the way it has been taken up and transformed by writers working in a Biblical tradition. Different ways to think about exemplarity are considered, particularly the theological distinction between likeness, image, and vestige, and between a likeness to a divine idea and a likeness to a divine perfection. Attention is given to the idea of the imago dei.

The final chapters of this book look at how a participatory outlook can inform and has informed a vision of the world and what it means to live, act, pray, and seek God in it. This, the first of these chapters, considers knowledge and knowing in participatory terms. Knowledge is seen as a participation of the knower in the known, or a sharing from the known to the knower. This undergirds a 'realist' epistemology, in that knowing rests on the reality of the thing that is known. That said, it also stresses the creaturehood and particularity of the knower and the manner of knowing: that which is known comes to be in the knower in the manner of the knower, whether we are talking about our knowledge of an animal, of a plant, or of God. In the case of God, most of all, the knower never exhausts the depths of what is known. That also applies, however, although to a different degree, in the knowledge of even mundane things, since their deepest reality is a participation in God, which confers a creaturely form of inexhaustibility. In these ways, much of this chapter is an exploration of 'intra-finite participation': about how one creature participates in, or donates to, another. It closes with a discussion of the relation between reason and revelation.