What is deification or theosis? – Clarification

Deification or theosis is the participation of man in the uncreated Divine Light (Met. Hierotheos, 2010, The science of spiritual medicine). Deification does not simply constitute “the forgiveness of sins through the Holy Spirit but man’s participation in the Holy Spirit. The forgiveness of sins is not the same as participation in the All-Holy Spirit” (ibid., p. 455). Deification has several levels to it because perfection, a key component of deification, is infinite.