“give to you...the land.” 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 promise God made to give the land to Abraham and his descendants, see commentary on Genesis 15:18].
“everlasting.” The Hebrew word is olam (#05769 עוֹלָם), and here and elsewhere it can mean “everlasting” or “age enduring,” or “of long duration.” The Hebrews did not have a word that meant “forever” like English does. English time words are very specific: “forever” means forever, while “of long duration,” or “for a long time,” means for a long time but not forever. However, the Hebrew word olam can mean forever or it can mean “for a long time.” In this case, the whole earth will be changed when the New Jerusalem comes from heaven (Rev. 21:1-2), and the land we now know will cease to exist. But it has been 4000 years since Abraham, and the Millennial Kingdom will add 1000 years to that, so God’s promise will certainly qualify as being “for a long time.”