A.T. Robertson Commentary Revelation 21:7

"He that overcometh shall inherit these things; and I will be his God, and he shall be my son." — Revelation 21:7 (ASV)

He that overcometh (ο νικων). Recalls the promises at the close of each of the Seven Letters in chapters 2 and 3.

Shall inherit (κληρονομησε). Future active of κληρονομεω, word with great history (1 Peter 1:4; Galatians 4:7; Romans 8:17), here interpreted for the benefit of these who share in Christ's victory.

I will be his God (Εσομα αυτω θεος). Repeated Old Testament promise (first to Abraham, Genesis 17:7f.). Cf. Revelation 21:3.

He shall be my son (αυτος εστα μο υιος). Made first of Solomon (2 Samuel 7:14) and applied to David later in Ps 89:26f.