A.T. Robertson Commentary Revelation 3:21

"He that overcometh, I will give to him to sit down with me in my throne, as I also overcame, and sat down with my Father in his throne." — Revelation 3:21 (ASV)

He that overcometh (ο νικων). Absolute nominative again as in 3:12, but resumed this time by the dative αυτω as in 2:26.

To sit (καθισα). First aorist active infinitive of καθιζω. This promise grows out of the prophecy that the saints will share in the Messiah's rule, made to the twelve (Matthew 19:28; Luke 22:29f.), repeated by Paul (1 Corinthians 6:2f.), enlarged in Re 22:1-5 (to last forever, 2 Timothy 2:11f.). James and John took this hope and promise literally not metaphorically.

As I also overcame (ως καγω ενικησα). First aorist active indicative of νικαω, looking back on the victory as over in the past. In Joh 16:33 before the Cross Jesus says Εγω νενικηκα τον κοσμον (perfect active), emphasizing the abiding effect of the victory.

Sat down (εκαθισα). "I took my seat" (Hebrews 1:3) where Christ is now (Revelation 22:3; Colossians 3:1). Cf. 1 John 5:4; Revelation 2:27f. Each of these seven messages begins alike and ends alike. Each is the message of the Christ and of the Holy Spirit to the angel of the church. Each has a special message suited to the actual condition of each church. In each case the individual who overcomes has a promise of blessing. Christ the Shepherd knows his sheep and lays bare the particular peril in each case.