Genesis 13:14-18

¹⁴ And the Lord said unto Abram, after that Lot was separated from him, Lift up now thine eyes, and look from the place where thou art northward, and southward, and eastward, and westward:

¹⁵ For all the land which thou seest, to thee will I give it, and to thy seed for ever.

¹⁶ And I will make thy seed as the dust of the earth: so that if a man can number the dust of the earth, then shall thy seed also be numbered.

¹⁷ Arise, walk through the land in the length of it and in the breadth of it; for I will give it unto thee.

¹⁸ Then Abram removed his tent, and came and dwelt in the plain of Mamre, which is in Hebron, and built there an altar unto the Lord.

God in grace once again confirmed His covenant with Abram to give him the land. … Abram never actually owned the land himself, however, during his lifetime. Nor, for most of human history, have his descendants actually owned the land, especially those of the promised seed, Isaac. … Since God promised the land to Abram and his seed forever, this can ultimately … be fulfilled only in the new earth of Revelation 21. It will … be fulfilled precursively, however, during the coming millennial age. 

God also assured Abram again that He would make him a great nation, with his seed numbering “as the dust of the earth.” The descendants of Abram today include not only the Jews but also the Arabs, and the number indeed is great. Once again, though, for the promise to be strictly literal, there must be a future fulfillment. During the Millennium, according to Revelation 20:8, earth’s population will be “as the sand of the sea.” Since it would be physically impossible to have as many people on earth as there are grains of sand (say, perhaps a billion billion), this expression evidently is a figure of speech for a number too great for actual enumeration. [But] there is no reason to doubt the reality of its promised literal fulfillment. God does not break His word, nor change His mind, and this promise was given unconditionally. Abram … was promised a nation that would bless other nations. — Morris, page 305

Abram pulled up his tent again and descended from the mountain into the plain of Mamre (or the terebinth “grove of Mamre,” as rendered by the newer versions) near Hebron. Hebron, of course, was not yet in existence as a city by that name (Numbers 13:22), so this reference to Hebron should be understood as an editorial insertion by Moses into Isaac’s “generations” document to identify the location for future readers. The same will be found true of a number of other localities mentioned in Genesis.

Here in Mamre (so named after an Amorite chieftain who had settled there earlier—see Genesis 14:13), Abram built another altar. This was to be his home for some time now, and he wanted a place where his family and servants could meet for formal worship of God. — Morris, page 306.