In the early church, catechumens were persons undergoing instruction prior to baptism.
The Greeks, having arrested the slaves of Christian catechumens, used force against them. Ecumenius, citing Irenaeus (c. 180, E/W), 1.570.
The young catechumen is imbued with perception and thought. Clement of Alexandria (c. 195, E), 2.510.
To begin with, it is doubtful [among the heretics] who is a catechumen and who is a believer. They all have access alike, they hear alike, and they pray alike. Tertullian (c. 197, W), 3.263.
Let no one, then, falter because of being assigned to the new recruit classes of hearers—as if on that account he has a license now even to sin. As soon as you know the Lord, you should fear Him. As soon as you have gazed on Him, you should reverence Him. For what difference does your knowing Him make, if you continue in the same practices as in bygone days—when you did not know Him? Furthermore, what is it that distinguishes you from a perfected servant of God? Is there one Christ for the baptized and another for the hearers? Tertullian (c. 203, W), 3.661, 662.
It is good that learners desire baptism, but do not hastily receive it. For he who desires it, honors it. He who hastily receives it, disdains it. . . . Hasty reception is the portion of irreverence. It inflates the seeker; it despises the Giver. And thus it sometimes deceives, for it promises to itself the gift before it is due. Tertullian (c. 203, W), 3.662.
[INSTRUCTIONS TO CATECHUMENS:] I admonish all believers in Christ, who have forsaken idols, for your salvation. . . . Let the mind be watchful of good things. Beware that you do not fall into former sins. In baptism, the coarse garment of your birth is washed. For if any sinful catechumen is marked with punishment, let him live in the signs, although not without loss. The whole of the matter for you is this: always shun great sins. Commodianus (c. 240, W), 4.212.
You see in the congregation of what is more commonly called the church the catechumens dispersed behind those who are at the extreme end of it. Origen (c. 245, E), 9.447.
There are certain doctrines that are not made known to the multitude. Rather, they are [revealed to the few] after the outsiders have been taught. But this is not a peculiarity of Christianity alone, but also of philosophic systems. Origen (c. 248, E), 4.399.
Christians test beforehand the souls of those who wish to become their hearers. First, we instruct them in private. Once they appear to have sufficiently demonstrated their desire towards a virtuous life, then we introduce them [to other Christians]—but not before. Next, we privately form one class of those who are beginners. These are the ones who are receiving admission, but who have not yet obtained the mark of complete purification. And we form another class of those who have manifested to the best of their ability their intention to desire no other things than what are approved by Christians. Among these, there are certain persons appointed to make inquiries regarding the lives and behavior of those who join them—so that they can prevent those who commit acts of infamy from coming into their public assembly. However, those of a different character, they receive with their whole heart, in order that they may daily make them better. Origen (c. 248, E), 4.484, 485.
We do everything in our power to secure that our meetings should be composed of wise men. We then venture to bring forward publicly in our discussions those things among us that are especially excellent and divine. That is, when we have an abundance of intelligent hearers. However, we conceal and pass by in silence the truths of deeper importance when we see that our audience is composed of simpler minds, who need such instruction as is figuratively called milk. Origen (c. 248, E), 4.485.
He who acts as an initiator . . . will say to those who have been purified in heart: “He whose soul has, for a long time, been conscious of no evil—particularly since he yielded himself to the healing of the word—let such a person hear the doctrines that were spoken in private by Jesus to His genuine disciples.” Origen (c. 248, E), 4.488.
The catechumen should now sin no longer. Cyprian (c. 250, W), 5.554.
If they have departed this life, they are considered to be in the number of those who have been catechumens among us, but who died before they were baptized. Of course, they had attained no small advantage of truth and faith by forsaking error. However, they were prevented by death from gaining the consummation of grace. Firmilian (c. 256, E), 5.395.
The church now declares these mysteries to you who are transferred from the roles of the catechumens. However, it is not her custom to declare them to the Gentiles. For we do not declare the mysteries concerning the Father, the Son, and the Holy Spirit to a Gentile. Neither do we speak of the mysteries plainly in the presence of the catechumens. Disputation of Archelaus and Manes (c. 320, E), 6.235.
Instruct the catechumens in the elements of religion and then baptize them. Apostolic Constitutions (compiled c. 390, E), 7.457.
Let him . . . be instructed before his baptism in the knowledge of the unbegotten God, in the understanding of His Only Begotten Son, and in the assured acknowledgement of the Holy Spirit. Apostolic Constitutions (compiled c. 390, E), 7.475.
Let him who is to be a catechumen be a catechumen for three years. However, if anyone is diligent and has a good-will to his earnestness, let him be admitted [to baptism]. For it is not the length of time that is to be judged, but the course of life. Apostolic Constitutions (compiled c. 390, E), 7.495; extended discussion of subjects to be taught to the catechumen: 7.475, 476.