"And if they are not to be blamed for so doing, let us see whether Christians do not exhort multitudes to the practice of virtue in a greater and better degree than they. For the philosophers who converse in public do not pick and choose their hearers, but he who likes stands and listens. The Christians, however, having previously, so far as possible, tested the souls of those who wish to become their hearers, and having previously instructed them in private, when they appear (before entering the community) to have sufficiently evinced their desire towards a virtuous life, introduce them then, and not before, privately forming one class of those who are beginners, and are receiving admission, but who have not yet obtained the mark of complete purification; and another of those who have manifested to the best of their ability their intention to desire no other things than are approved by Christians"Origen
Against Celsus Bk. III Ch. LI, Vol. 4

"Let him, therefore, who is to be taught the truth regarding piety be instructed before his baptism in the knowledge of the unbegotten God, in the understanding of His only begotten Son, in the assured acknowledgment of the Holy Ghost. Let him learn the order of the several parts of the creation, the series of providence, the different dispensations of Thy laws."Constitution of the Apostles
Bk. 7 Pt. 2 Ch. XXXIX, Vol. 7

"“He whose soul has, for a long time, been conscious of no evil, and especially since he yielded himself to the healing of the word, let such an one hear the doctrines which were spoken in private by Jesus to His genuine disciples.” Therefore in the comparison which he institutes between the procedure of the initiators into the Grecian mysteries, and the teachers of the doctrine of Jesus, he does not know the difference between inviting the wicked to be healed, and initiating those already purified into the sacred mysteries!"Origen
Against Celsus Bk. III Ch. LX, Vol. 4

But prophecy does not employ figurative forms in the expressions for the sake of beauty of diction. But from the fact that truth appertains not to all, it is veiled in manifold ways, causing the light to arise only on those who are initiated into knowledge, who seek the truth through love. The proverb, according to the Barbarian philosophy, is called a mode of prophecy, and the parable is so called, and the enigma in addition. Further also, they are called “wisdom;” and again, as something different from it, “instruction and words of prudence,” and “turnings of words,” and “true righteousness;” and again, “teaching to direct judgment,” and “subtlety to the simple,” which is the result of training, “and perception and thought,” with which the young catechumen is imbued. (Pro_1:1-4) “He who bears these prophets, being wise, will be wiser. And the intelligent man will acquire rule, and will understand a parable and a dark saying, the words and enigmas of the wise.”Clement
Stromata Bk. 6 Ch. XV, Vol. 2

"That the catechumen ought now no longer to sin. In the Epistle of Paul to the Romans: “Let us do evil until the good things come; whose condemnation is just.” (Rom_3:8)"Cyprian
Treatise of Cyprian Treatise XII Vol. 5

“These mysteries, which the Church now declares to you who are transferred from the lists of the catechumens, it is not her custom to declare to the Gentiles. For we do not declare the mysteries touching the Father, and the Son, and the Holy Spirit to a Gentile; neither do we speak of the mysteries plainly in presence of the catechumens;”Archelaus
Acts of Disputation Vol. 6

In few words, I admonish all believers in Christ, who have forsaken idols, for your salvation. In the first times, if in any way thou fallest into error, still, when entreated, do thou leave all things for Christ; and since thou hast known God, be a recruit good and approved, and let virgin modesty dwell with thee in purity. Let the mind be watchful for good things. Beware that thou fall not into former sins. In baptism the coarse dress of thy birth is washed. For if any sinful catechumen is marked with punishment, let him live in the signs of Christianity, although not without loss. The whole of the matter for thee is this, do thou ever shun great sins.Commodianus
Instructions Ch. XLVI, Vol. 4

“And when it remains that the catechumen is to be baptized, let him learn what concerns the renunciation of the devil, and the joining himself with Christ; for it is fit that he should first abstain from things contrary, and then be admitted to the mysteries. He must beforehand purify his heart from all wickedness of disposition, from all spot and wrinkle, and then partake of the holy things;”Constitutions of the Apostles
Bk. 7 Pt. 2 Ch. XL, Vol. 7

"Let him who is to be a catechumen be a catechumen for three years; but if anyone be diligent, and has a good-will to his business, let him be admitted: for it is not the length of time, but the course of life, that is judged."Constitution of the Apostles
Bk. 8 Pt. 2 Ch. XXXII, Vol. 7

"I must not omit an account of the conduct also of the heretics - how frivolous it is, how worldly, how merely human, without seriousness, without authority, without discipline, as suits their creed. To begin with, it is doubtful who is a catechumen, and who a believer; they have all access alike, they hear alike, they pray alike - even heathens, if any such happen to come among them. “That which is holy they will cast to the dogs, and their pearls,” although (to be sure) they are not real ones, “they will fling to the swine.” (see Mat_7:6)"Tertullian
Remedy Against Heretics Ch. XLI, Vol. 3

"In baptism the coarse dress of thy birth is washed. For if any sinful catechumen is marked with punishment, let him live in the signs of Christianity, although not without loss.13 The whole of the matter for thee is this, Do thou ever shun great sins."Commodianus
The Octavius Ch. XLVI, Vol. 4

"But he who acts as initiator, according to the precepts of Jesus, will say to those who have been purified in heart, “He whose soul has, for a long time, been conscious of no evil, and especially since he yielded himself to the healing of the word, let such an one hear the doctrines which were spoken in private by Jesus to His genuine disciples.” Therefore in the comparison which he institutes between the procedure of the initiators into the Grecian mysteries, and the teachers of the doctrine of Jesus, he does not know the difference between inviting the wicked to be healed, and initiating those already purified into the sacred mysteries!"Origen
Against Celsus Bk. III Ch. LX, Vol. 4

"For when the Greeks, having arrested the slaves of Christian catechumens, then used force against them, in order to learn from them some secret thing [practiced] among Christians, these slaves, having nothing to say that would meet the wishes of their tormentors, except that they had heard from their masters that the divine communion was the body and blood of Christ, and imagining that it was actually flesh and blood, gave their inquisitors answer to that effect. Then these latter, assuming such to be the case with regard to the practices of Christians, gave information regarding it to other Greeks, and sought to compel the martyrs Sanctus and Blandina to confess, under the influence of torture, [that the allegation was correct]. To these men Blandina replied very admirably in these words: “How should those persons endure such [accusations], who, for the sake of the practice [of piety], did not avail themselves even of the flesh that was permitted [them to eat]?”"Iranaeus
Fragments Ch. XIII, Vol. 1

"After this, let all rise up with one consent, and looking towards the east, after the catechumens and penitents are gone out, pray to God eastward, who ascended up to the heaven of heavens to the east; remembering also the ancient situation of paradise in the east, from whence the first man, when he had yielded to the persuasion of the serpent, and disobeyed the command of God, was expelled."Apostolic Constitution
Bk. 2 Pt. 3 Ch. LVII, Vol. 7