The religious, theological and philosophical discourse in Late Antiquity concerning the human soul, the Greek psuchē, reveals a sophisticated and complex psychological language that was aimed at conceptualizing and articulating the act of conversion. The analysis of Gnostic, Orthodox Christian, and Neoplatonic writings in relation to the psuchē shows the cardinal role that this term played in formulating individual processes of mental transformation. Attributing active agency, mutability and relational aspect to the individual psuchē turned it into a unique conceptual device, necessary to define anew the human condition.