All ideals of Christian perfection, and mysticism is certainly one of these, are forms of response to the presence of God, a presence that is not open, evident, or easily accessible, but that is always in some way mysterious or hidden. When that hidden presence becomes the subject of some form of immediate experience, we can perhaps begin to speak of mysticism in the proper sense of the term. The responses of the subject to immediate divine presence have been discussed theologically in a variety of ways and according to a number of different models. Among them we might list direct contemplation or vision of God, rapture or ecstasy, deification, living in Christ, the birth of the Word in the soul, radical obedience to the directly present will of God, and especially union with God. All of these responses, which have rarely been mutually exclusive, can be called mystical in the sense that they are answers to the immediately experienced divine presence. Therefore, the mysticism of union is just one of the species of a wider and more diverse genus or group.