“I have given this land.” We would say, “I will give this land,” because the promise will be fulfilled in the future. The Hebrew text and translation use the Hebrew idiom of the prophetic perfect, which occurs when something that is future is spoken of as if it is in the past in order to emphasize the certainty that it will happen. God was absolutely going to give the land to the descendants of Abraham, so He said He had already given it to them. This prophecy was fulfilled in part at times in Israel’s history, and it will be ultimately fulfilled in Christ’s Millennial Kingdom on earth.
God repeated the promise that He would give the land of Israel to Abraham and his descendants many times, and said it in slightly different ways. He told Abraham that he and his descendants would get the land (Gen. 12:7; 13:15-17; 15:7, 18; 17:8). He told it to Isaac (Gen. 26:3). He told it to Jacob (Gen. 28:13; 35:12; 48:4). Then over and over He told Israel about the promise or that He would give them the land (cp. Exod. 6:4, 8; 12:25; 13:5, 11; Lev. 14:34; 20:24; 23:10; 25:2).
[For more on the prophetic perfect idiom, see commentary on Ephesians 2:6. For more on the Millennial Kingdom on earth during which time God’s promise will be completely fulfilled, see Appendix 3: “Christ’s Future Kingdom on Earth”].