John Chrysostom, on 1Cor 10:12

"Wherefore let him that thinketh he standeth take heed lest he fall."

Again, he casts down their pride who thought highly of their knowledge. For if they who had so great privileges suffered such things; and some for murmuring alone were visited with such punishment, and others for tempting, and neither their multitude moved God to repent, nor their having attained to such things; much more shall it be so in our case, except we be sober. And well said he, "he that thinketh he standeth:" for this is not even standing as one ought to stand, to rely on yourself: for quickly will such an one fall: since they too, had they not been high-minded and self-confident, but of a subdued frame of mind, would not have suffered these things. Whence it is evident, that chiefly pride, and carelessness from which comes gluttony also, are the sources of these evils. Wherefore even though thou stand, yet take heed lest thou fall. For our standing here is not secure standing, no not until we be delivered out of the waves of this present life and have sailed into the tranquil haven. Be not therefore high-minded at thy standing, but guard against thy falling; for if Paul feared who was firmer than all, much more ought we to fear.

Now the Apostle's word, as we have seen, was, "Wherefore let him that thinketh he standeth take heed lest he fall;" but we cannot say even this; all of us, so to speak, having fallen, and lying prostrate on the ground. For to whom am I to say this? To him that committeth extortion every day? Nay, he lies prostrate with a mighty fall. To the fornicator? He too is cast down to the ground. To the drunkard? He also is fallen, and knoweth not even that he is fallen. So that it is not the season for this word, but for that saying of the prophet which he spake even to the Jews, "He that falleth, doth he not rise again?" For all are fallen, and to rise again they have no mind. So that our exhortation is not concerning the not falling, but concerning the ability of them that are fallen to arise. Let us rise again then, late though it be, beloved, let us rise again, and let us stand nobly.