Clement of Alexandria — Stromata 16

But those who are ready to toil in the most excellent pursuits, will not desist from the search after truth , till they get the demonstration from the Scriptures themselves. There are certain criteria common to men , as the senses; and others that belong to those who have employed their wills and energies in what is true — the methods which are pursued by the mind and reason, to distinguish between true and false propositions. Now, it is a very great thing to abandon opinion, by taking one's stand between accurate knowledge and the rash wisdom of opinion, and to know that he who hopes for everlasting rest knows also that the entrance to it is toilsome and strait.

And let him who has once received the Gospel , even in the very hour in which he has come to the knowledge of salvation , not turn back, like Lot's wife, as is said; and let him not go back either to his former life, which adheres to the things of sense, or to heresies . For they form the character, not knowing the true God. For he that loves father or mother more than Me, the Father and Teacher of the truth , who regenerates and creates anew, and nourishes the elect soul , is not worthy of Me — He means, to be a son of God and a disciple of God , and at the same time also to be a friend, and of kindred nature. For no man who looks back, and puts his hand to the plough, is fit for the kingdom of God .

Luke 9:62 But, as appears, many even down to our own time regard Mary, on account of the birth of her child, as having been in the puerperal state, although she was not. For some say that, after she brought forth, she was found, when examined, to be a virgin . Now such to us are the Scriptures of the Lord, which gave birth to the truth and continue virgin, in the concealment of the mysteries of the truth . And she brought forth, and yet brought not forth, says the Scripture ; as having conceived of herself, and not from conjunction. Wherefore the Scriptures have conceived to Gnostics ; but the heresies , not having learned them, dismissed them as not having conceived.

Now all men , having the same judgment, some, following the Word speaking, frame for themselves proofs ; while others, giving themselves up to pleasures, wrest Scripture, in accordance with their lusts . And the lover of truth , as I think, needs force of soul . For those who make the greatest attempts must fail in things of the highest importance; unless, receiving from the truth itself the rule of the truth , they cleave to the truth . But such people, in consequence of falling away from the right path, err in most individual points; as you might expect from not having the faculty for judging of what is true and false, strictly trained to select what is essential. For if they had, they would have obeyed the Scriptures .