1 In this portion of the holy Gospel, where the Lord says to His disciples, “I have yet many things to say unto you, but you cannot bear them now,” there meets us first this subject of needful inquiry, how it was that He said a little before, “All things that I have heard of my Father I have made known unto you,” and yet says here, “I have yet many things to say unto you, but you cannot bear them now.” But how it was that He spoke of what He had not yet done as if it were done, just as the prophet testifies that God has made those things which are still to come, when He says, “Who has made those things which are still to come,” we have already explained as well as we could when dealing with those words themselves.
Now, however, you are perhaps wishing to know what those things were which the apostles were then unable to bear. But which of us would venture to assert his own present capacity for what they wanted the ability to receive? And on this account you are neither to expect me to tell you things which perhaps I could not comprehend myself were they told me by another; nor would you be able to bear them, even were I talented enough to let you hear of things that are above your comprehension.
It may be, indeed, that some among you are fit enough already to comprehend things which are still beyond the grasp of others; and if not all about which the divine Master said, “I have yet many things to say unto you,” yet perhaps some of them: but what they were which He Himself thus omitted to tell them, it would be rash to have even the wish to presume to say. For at that time the apostles were not yet fitted even to die for Christ, when He said to them, “You cannot follow me now,” and when the very foremost of them, Peter, who had presumptuously declared that he was already able, met with a different experience from what he anticipated: and yet afterwards a countless number both of men and women, boys and girls, youths and maidens, old and young, were crowned with martyrdom; and the sheep were found able for that which, when the Lord spoke these words, the shepherds were still unable to bear.
Ought, then, those sheep to have been asked, in that extremity of trial, when required to contend for the truth even unto death, and to shed their blood for the name or doctrine of Christ;— ought they, I say, to have been asked, Which of you would venture to account himself ready for martyrdom, for which Peter was still unfitted, even when taught face to face by the Lord Himself? In the same way, therefore, one may say that Christian people, even when desiring to hear, ought not to be told what those things are of which the Lord then said, “I have yet many things to say unto you, but you cannot bear them now.”
If the apostles were still unable, much more so are you: although it may be that many now can bear what Peter then could not, in the same way as many are able to be crowned with martyrdom which at that time was still beyond the power of Peter, more especially that now the Holy Spirit has been sent, as He was not then, of whom He went on immediately to add the words, “Howbeit when He, the Spirit of truth, has come, He will teach you all truth,” thereby showing of a certainty that they could not bear what He had still to say, because the Holy Spirit had not yet come upon them.
Source: Tractates on the Gospel of John (New Advent)