Thomasius's interest in the reform of the corrupt will-as-desire was not important only because of religious faith or the influence of the clergy on secular jurisdiction. Thomasius also believed that temporal morality and happiness were based on the same reformed state of the will as religious belief, because a pious individual was free from the corrupting passions, which were the cause of sin and unease in the unregenerate. When the “scholastic” orthodox theologians reduced faith to doctrinal opinions in the intellect, this affected their moral philosophy, too, because it led them to ignore the importance of the will-as-desire for achieving moral virtue.

In his first work on natural law, the Institutes of Divine Jurisprudence of 1688, Thomasius had not yet adopted this belief in the importance of the human will-as-desire, but by the time he published his second treatise on natural jurisprudence, the Foundations of the Law of Nature and Nations, in 1705, the reform of the human will-as-passion had become central to his theory of moral conduct. This transformation of Thomasius's natural jurisprudence was to some extent a reflection of the changes in his notion of faith and his anthropology during the 1690s. It was, however, also symptomatic of a much broader trend in the moral philosophy of the early Enlightenment and the status of the passions within it. This was a development from a belief that actions motivated by passions were necessarily opposed to morality to a belief that moral actions were themselves motivated by certain kinds of passions. Samuel Pufendorf, for example, had argued in his On the Law of Nature and Nations of 1672 that the subject of natural jurisprudence was laws imposed by God on humanity. The passions, Pufendorf believed, were not part of this morality but an obstacle to it, because they distorted the judgment by the intellect and restricted the freedom of the will, which was essential for the ability to choose what was morally good.