John Gill Commentary Genesis 13:15

"for all the land which thou seest, to thee will I give it, and to thy seed for ever." — Genesis 13:15 (ASV)

For all the land which you see, to you will I give it , &c.] Not only so much of it as his eye could reach, but all of it, as far as it went, which way soever he looked; and this he gave him to sojourn in now where he pleased, and for his posterity to dwell in hereafter; he gave him the title to it now, and to them the possession of it for future times:

and to your seed for ever; the meaning is, that he gave it to his posterity to be enjoyed by them until the Messiah came, when a new world would begin; and which Abram in person shall enjoy, with all his spiritual seed, after the resurrection, when that part of the earth will be renewed, as the rest; and where particularly Christ will make his personal appearance and residence, the principal seed of Abram, and will reign a thousand years; (See Gill on Matthew 22:32);

besides, this may be typical of the heavenly Canaan given to Abram, and all his spiritual seed, and which shall be enjoyed by them for evermore.