2 I told you before, and foretell you, as if I were present, the second time; and being absent now I write to them which heretofore have sinned, and to all other, that, if I come again, I will not spare:
Is he then the same God as He who gave Satan power over the person of Job that his "strength might be made perfect in weakness? " How is it that the censurer of the Galatians still retains the very formula of the law: "In the mouth of two or three witnesses shall every word be established? " How again is it that he threatens sinners "that he will not spare" them -he, the preacher of a most gentle god? Yea, he even declares that "the Lord hath given to him the power of using sharpness in their presence!" Deny now, O heretic, (at your cost, ) that your god is an object to be feared, when his apostle was for making himself so formidable!
That all sins may be forgiven him who has turned to God with his whole heart... Also in the same [second Epistle of the blessed Paul to the Corinthians]: "I told you before, and foretell you as I sit present; and absent now from those who before have sinned, and to all others; as, ill shall come again, I will not spare."
"For if at the mouth of two witnesses or three every word shall be established, and I have come twice and spoken, and speak now also by this Epistle; it follows, I must after this keep my word. For think not, I pray you, that my writing is of less account than my coming; for as I spoke when present, so now I write also when absent." Seest thou his fraternal solicitude? Seest thou forethought becoming a teacher? He neither kept silence nor punished, but he both foretells often, and continues ever threatening, and puts off the punishment, and if they should continue unamended, then he threatens to bring it to the proof.
Having showed before that he is unable to do this unless he is compelled, and having called the thing a mourning, and a humbling; (for he saith, "lest my God should humble me before you, and I should mourn for them that have sinned heretofore, and not repented;") and having made his excuse unto them, namely, that he had told them before, once and twice and thrice, and that he does and contrives all he can so as to hold back the punishment, and by the fear of his words to make them better, he then used this unpleasing and terrifying expression, "If I come again, I will not spare." He did not say, "I will avenge and punish and exact satisfaction:" but again expresses even punishment itself in paternal language; showing his tender affection, and his heart to be grieved along with them; because that he always to "spare" them put off.
Then that they may not think now also that there will be again a putting off, and merely a threat in words, therefore he both said before, "At the mouth of two witnesses or three shall every word be established;" and [now], "If I come again, I will not spare." Now what he means is this: "I will no longer put off, if (which God forbid) I find you unamended; but will certainly visit it, and make good what I have said."
[AD 220] Tertullian on 2 Corinthians 13:2