The Greek verb katēcheō means to instruct, teach orally, or inform — specifically to transmit knowledge through spoken instruction. It is the root of the English words 'catechism' and 'catechize.' The prefix kata- (down) + ēcheō (to sound) suggests instruction that 'sounds down into' the listener.
Katēcheō appears at several pivotal moments in Acts and the Epistles. Apollos had been 'instructed in the way of the Lord' (Acts 18:25) but knew only John's baptism — a reminder that even thorough catechetical training can be incomplete and require deepening. Luke's prologue addresses Theophilus, who had already received some instruction (katēcheō) and is now given a reliable, ordered account (Luke 1:4). Galatians 6:6 establishes the principle: 'Anyone who receives instruction (katēchoumenos) in the word should share all good things with their instructor.' This verse is foundational for pastoral compensation and the concept of theological apprenticeship. The entire tradition of catechesis flows from this word.