Mark 9:1

(Orig. in Matt. tom. xii. 33, 35) But in a mystical sense, Christ is life, and the devil is death, and he tastes of death, who dwells in sin; even now every one, according as he has good or evil doctrines, tastes the bread either of life or of death. And indeed, it is a less evil to see death, a greater to taste of it, still worse to follow it, worst of all to be subject to it.

(Hom. in Matt. 56) And He did not declare the names of those who were about to go up, lest the other disciples should feel some touch of human frailty, and He tells it to them beforehand, that they might come with minds better prepared to be taught all that concerned that vision.

(in Marc. 3. 36) Truly it was done with a loving foresight, in order that they, having tasted for a brief moment the contemplation of everlasting joy, might with the greater strength bear up under adversity.

(ubi sup.) Or else the present Church is called the kingdom of God; and some of the disciples were to live in the body until they should see the Church built up, and raised against the glory of the world; for it was right to make some promises concerning this life to the disciples who were uninstructed, that they might be built up with greater strength for the time to come.

But because He had spoken of His glory, in order to show that His promises were not vain, He subjoins, Verily I say unto you, That there be some of them that stand here who shall not taste of death, till they have seen the kingdom of God come with power. As if He said, Some, that is, Peter, James, and John, shall not taste of death, until I show them, in my transfiguration, with what glory I am to come in my second advent; for the transfiguration was nothing else, but an announcement of the second coming of Christ, in which also Christ Himself and the Saints will shine.