John Lightfoot on Mark 9:1

[The kingdom of God coming in power.] In Matthew, it is the Son of man coming in his kingdom. The coming of Christ in his vengeance and power to destroy the unbelieving and most wicked nation of the Jews is expressed under these forms of speech. Hence the day of judgment and vengeance:

I. It is called "the great and terrible day of the Lord," Acts 2:20; 2 Thess 2:2,3.

II. It is described as "the end of the world," Jeremiah 4:27; Matthew 24:29, &c.

III. In that phrase, "in the last times," Isaiah 2:2; Acts 2:17; 1 Tim 4:1; 2 Peter 3:3; that is, in the last times of that city and dispensation.

IV. Thence, the beginning of the "new world," Isaiah 65:17; 2 Peter 3:13.

V. The vengeance of Christ upon that nation is described as his "coming," John 21:22; Hebrews 10:37: his "coming in the clouds," Revelation 1:7: "in glory with the angels," Matthew 24:30, &c.

VI. It is described as the 'enthroning of Christ, and his twelve apostles judging the twelve tribes of Israel,' Matthew 19:28; Luke 22:30.

Hence this is the sense of the present place: Our Saviour had said in the last verse of the former chapter, "Whosoever shall be ashamed of me and of my words in this adulterous and sinful generation; of him also shall the Son of man be ashamed, when he cometh in the glory of his Father with the holy angels," to take punishment of that adulterous and sinful generation. And he suggests, with good reason, that that his coming in glory should be in the lifetime of some that stood there.