1 Thessalonians 3:10

But to those who are still babes in mind, and who as carnal, the apostle says, require to be nourished with milk, all discoursing on such a subject, wherein we deal not only with the believing, but also with the understanding and the knowing of what is spoken, must be burdensome, as being still unable to perceive such things, and be more fitted to oppress than to feed them. Whence it comes to pass that the spiritual, while not altogether silent on such subjects to the carnal, because of the Catholic faith which is to be preached to all, yet do not so handle them as, in their wish to simplify them to understandings that are still deficient in capacity, to bring their discourse on the truth into disrepute, rather than the truth that is in their discourse within the perceptions of their hearers. Accordingly in his Epistle to the Colossians he says: "And though I be absent in the flesh, yet am I with you in the spirit, joying and beholding your order, and that which is lacking in your faith in Christ." And in that to the Thessalonians: "Night and day," he says, "praying more abundantly, that we might see your face, and might perfect that which is lacking in your faith."

"For what thanksgiving can we render again unto God for you, for all the joy wherewith we joy for your sakes before our God; night and day praying exceedingly that we may see your face, and may perfect that which is lacking in your faith?" Not only, he says, are ye the causes of life to us, but also of much joy, and so much that we cannot worthily give thanks to God. Your good behavior, he says, we consider to be the gift of God. Such kindnesses have you shown to us, that we think it to be of God; yea, rather, and it is of God. For such a disposition of mind comes not of a human soul or carefulness. "Night and day," he says, "praying exceedingly." This too is a sign of joy. For as any husbandman, hearing concerning his land that has been tilled by himself, that it is burdened with ears of grain, longs with his own eyes to see so pleasant a sight, so Paul to see Macedonia. "Praying exceedingly." Observe the excess; "that we may see your face, and may perfect that which is lacking in your faith." Here there is a great question. For if now thou livest, because they stand fast, and Timothy brought thee "glad tidings of their faith and love," and thou art full of so much joy as not to be able worthily to give thanks to God, how sayest thou here that there are deficiencies in their faith? Were those then the words of flattery? By no means, far be it. For previously he testified that they endured many conflicts, and were no worse affected than the Churches in Judaea. What then is it? They had not enjoyed the full benefit of his teaching, nor learned all that it behoved them to learn. And this he shows toward the end. Perhaps there had been questionings among them concerning the Resurrection, and there were many who troubled them, not by temptations, nor by dangers, but by acting the part of teachers. This is what he says is lacking in their faith, and for this reason, he has so explained himself, and has not said, that you should be confirmed, where indeed he feared concerning the faith itself, "I have sent," he says, "Timothy to confirm you," but here, "to perfect that which is lacking," which is rather a matter of teaching than of confirming.