This paper traces the evolution of catechesis in ancient Christianity, from early apostolic gatherings focused on Jesus's teachings to a highly structured Patristic catechumenate. This organized system involved rigorous doctrinal and moral formation, multiple scrutinies, Lenten preparation, and the reception of the Sacraments of Initiation during the Easter vigil. However, when Christianity became the official imperial religion, the catechumenate declined. Driven by insincere conversions, delayed baptisms, and an increase in infant baptisms, the process shortened, shifting from a comprehensive school of Christian living into a brief preparation for sacramental rituals.