John Chrysostom, on 1Cor 14:20

As might be expected, after his long argument and demonstration he adopts a more vehement style and abundance of rebuke; and mentions an example suited to the subject. For children too are wont to gape after trifles and to be fluttered, but of things very great they have not so much admiration. Since then these also having the gift of tongues, which has the lowest of all, thought they had the whole; therefore he saith, "Be not children," i. e., be not without understanding where ye ought to be considerate, but there be ye childlike and simple, where unrighteousness is, where vain-glory, where pride. For he that is a babe in wickedness ought also to be wise. Since as wisdom with wickedness would not be wisdom, so also simplicity with folly would not be simplicity, it being requisite both in simplicity to avoid folly, and in wisdom wickedness. For as neither bitter nor sweet medicines in excess do good, so neither doth simplicity by itself, nor wisdom: and this is why Christ enjoining us to mix both said, "Be ye wise as serpents, and harmless as doves."

But what is it to be a babe in wickedness? Not even to know what wickedness is: yea, such he willed them to be. Wherefore also he said, "It is actually reported that there is fornication among you." He said not, "is done," but is "reported:" as if he said, "ye are not without knowledge of the thing; ye have heard of it some time." I say, he would have them both to be men and children; the one however in wickedness, but the other in wisdom. For so even the man may become a man, if he be also a child: but as long as he is not a child in wickedness, neither will he be a man. For the wicked, instead of being mature, will be but a fool.