In Matthew 16:28 Jesus promises his disciples, “Truly, I say to you, there are some standing here who will not taste death until they see the Son of Man coming in his kingdom.” What did Jesus mean? To which coming was he referring, because his Second Coming still has not occurred?

Norman Geisler and Thomas Howe offer three alternatives in When Critics Ask : A Popular Handbook on Bible Difficulties:

First, some have suggested that this may be a reference to the Day of Pentecost where Christ’s Helper, the Holy Spirit, came to descend upon the apostles. In John’s Gospel (14:26), Jesus promised to send the Holy Spirit, and, in the beginning of Acts (1:4–8), He tells them not to leave Jerusalem until they have received the Holy Spirit. But this hardly seems to fit the description of seeing Christ coming in His kingdom (Matt. 16:28).

Second, others believe this might be a reference to the destruction of Jerusalem and the temple in A.D. 70. This would mean that He would return to bring judgment upon the city that rejected Him and crucified Him. While this is a possible explanation, it does not seem to account for the fact that Jesus appears to be coming for believers (those ‘standing there’ with Him), not simply coming in judgment on unbelievers. Nor does the judgment on Jerusalem in A.D. 70 adequately express seeing the ‘Son of Man coming in His kingdom’ (v. 28), a phrase reminiscent of His second coming (cf. 26:64). Nor does it explain why Jesus never appeared in A.D. 70.

A third and more plausible explanation is that this is a reference to the appearance of Christ in His glory on the Mount of Transfiguration which begins in the very next verse (17:1). Here Christ does literally appear in a glorified form, and some of His apostles are there to witness the occasion, namely Peter, James, and John. This transfiguration experience, of course, was only a foretaste of His Second Coming when all believers will see Him come in power and great glory (cf. Acts 1:11; Rev. 1:7).

The authors of Hard Sayings of the Bible differ somewhat from Geisler and Howe. Here is their approach to the question:

With the death and exaltation of Jesus and the coming of the Spirit on the day of Pentecost following, some of those who were witnesses of his mighty works in Galilee and elsewhere saw the power of the kingdom of God manifested on a scale unmatched during his ministry. Within a few weeks, the number of his followers multiplied tenfold; his kingdom was visibly on the march.

This, at any rate, is an interpretation of his saying about the kingdom of God having come with power which makes it intelligible to us. Whether or not this interpretation coincides with his intention when he spoke in this way is a question to which it is best not to give a dogmatic answer.

The three Evangelists who record the saying (in varying terms) go on immediately to describe Jesus’ transfiguration, as though that event bore some relation to the saying (Mt 17:1–8; Mk 9:2–8; Lk 9:28–36). It cannot be said that the transfiguration was the event which Jesus said would come within the lifetime of some of his hearers; one does not normally use such language to refer to something that is to take place in a week’s time.

But the three disciples who witnessed the transfiguration had a vision of the Son of Man vindicated and glorified; they saw in graphic anticipation the fulfillment of his words about the powerful advent of the kingdom of God. Matthew, strikingly, in his report of the words speaks of the Son of Man instead of the kingdom of God: ‘there are some standing here who will not taste death before they see the Son of Man coming in his kingdom’ (Mt 16:28 RSV). This is an interpretation of the words, but a true interpretation. And Matthew follows Mark in saying that when the disciples had seen the vision, Jesus forbade them to speak about it to anyone ‘until the Son of man should have risen from the dead’ (Mk 9:9 RSV). His rising from the dead would inaugurate the reality which they had seen in the vision on the mount of transfiguration, and would at the same time herald the coming of the kingdom ‘with power.’

In my research on this question, most scholars follow Geisler and Howe: the transfiguration is the coming to which Jesus refers. However, a significant minority also note that Jesus’ resurrection and the Day of Pentecost are better answers to this question. We can agree that it is “best not to give a dogmatic answer.”