Noun
One who is receiving rudimentary instruction in the doctrines of Christianity; a neophyte; in the primitive church, one officially recognized as a Christian, and admitted to instruction preliminary to admission to full membership in the church.
Source: Webster's dictionary2. The catechumen or sponsors state their request for Baptism. Source: Internet
Thus for Aphraates baptism conditions the taking of a vow in which the catechumen promises celibacy. Source: Internet