The regular instruction of children began when they were twelve years old. " And Peter answered, "Do penance, and be baptized . It is both doctrinal and moral the hearers are to believe and to repent. Peter's second discourse after healing the lame man in the Temple (Acts 3). Stephen goes further, and brings out that belief in Jesus as the Christ (Messias) meant the ending of the Old Covenant and the coming in of a New (Acts 6:7). Philip the Deacon preached "of the kingdom of God, in the name of Jesus Christ"; and the Samaritans "were baptized, both men and women" (Acts 8). The same deacon's discourse to the eunuch deals with the proof from Scripture, and notably Isaias (53:7), that "Jesus Christ is the Son of God", and the necessity of baptism.
Thus we read of Christ "in the temple, sitting in the midst of the doctors, hearing them, and asking them questions. No mention is made of penance or repentance, as the eunuch was a just man anxious to do God's will.
Peter, except that Justin dwells on the Creation and proves the Divinity of Christ, the Logos and only-begotten Son of the Father.
(4) In the ages of persecution it became necessary to exercise great caution in admitting persons to membership in the Church.
The work of the Apologists had been to remove prejudices against Christianity, and to set forth its doctrines and practices in such a way as to appeal to the fair-minded pagan.
Even when he had been initiated, his instruction was not yet at an end. Cyril twenty-four catechetical discourses, forming together a complete course of moral and doctrinal instruction.
Him God raised up the third day, and gave him to be made manifest . To him all the prophets give testimony, that by his name all receive remission of sins, who believe in him" (Acts 10).
In this discourse we have the chief articles of the Creed: the Trinity (God, Jesus Christ "Lord of all things", the Holy Ghost), the Crucifixion, Death, and Resurrection of Our Lord; His coming to judge the living and the dead, and the remission of sins. Paul's discourses, though, of course, in addressing the pagans, whether peasants at Lystra or philosophers at Athens, he deals with the fundamental truths of the existence and attributes of God (Acts, xiii, xiv, xvii).
Luke's Gospel: "That thou mayest know the verity of those things in which thou hast been instructed" (] him, in all good things" (Galatians 6:6).
Hence the word, with its technical meaning of oral religious instruction, passed into ecclesiastical use, and is applied both to the act of instructing and the subject-matter of the instruction.