We are told, in 1Peter 1:10-12, that the prophets of old searched "what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow. Unto whom it was revealed, that not unto themselves, but unto us they did minister the things, which are now reported unto you ... with the Holy Ghost sent down from heaven".
They wrote of the sufferings, and they wrote of the glory that should follow; but there was nothing to tell them about the times or seasons. Whether the glory was to follow immediately on the sufferings, or whether there was to be an interval, and whether that interval was to be short or long, no hint was given. hence, they searched as to "what manner of time was signified".
This "time" refers to the "unsearchable riches of Christ". They could not them be traced. Even angels desire to look into these things (1Pet. 1:12).
"Now," all is revealed. It is ministered unto us, in the Scriptures of truth, on earth; and God is making known, by means of the Church, something of His manifold wisdom to the principalities and powers in the heavenly places (Eph. 3:9, 10).
Angels and prophets saw the "sufferings" like the tops of a distant mountain range -- while beyond it a farther range was seen in a distant haze of glory. But what lay between they could neither see nor know. But now it is revealed. The sufferings are past, and we are in the valley between these two mountain ranges. the glory is beyond. The secret "hid in God" has been made known; and we can understand, a little, the answer to the question of Christ to the two disciples : "Ought not Christ to have suffered these things, and to enter into His glory?" (Luke 24:26). They are linked together inseparably, especially in the first epistle of Peter. See 1Pet. 1:11; 3:18; 4:13; 5:1.
In the Old Testament they are each frequently dwelt upon together : but, we find that, while the glory is often mentioned and enlarged upon by itself, without any reference to the sufferings, we never find the sufferings mentioned without the glory being referred to immediately after. Sometimes the change is quite sudden. In Ps. 22, note the change from v. 21 to vv. 22-end. In Ps. 102, note the change from v. 11 to vv. 12-end. In Isa. 53 note the change in the middle of v. 10. (See Ap. 72.)
It seems that when the sufferings are mentioned, we are not left to think that all is to end there. The glory may be mentioned alone, because there is to be no end to it. But to the sufferings there was to be an end, and that end was to be revealed in glory.
That is why, when the Lord makes the first mention of His sufferings, in Matt. 16:21, He at once proceeded to speak of the time when He "shall come in the glory of His Father" (v. 27), and to add that some of those who were standing should see it. And then, after six days, three of them saw the power and coming of our Lord Jesus Christ, and were eye-witnesses of His majesty, when they were with Him in the holy mount (2Pet. 1:16-18. Cp. John 1:14).
Having heard of the sufferings, the disciples were not left to conclude that all was to end there : hence they were at once given the most wonderful exhibition of the glory which was to follow.
This is why the Transfiguration scene occurs in the third part of the Lord's ministry, which had to do with His sufferings. See notes on the Scriptures referred to above, and compareAp. 72.