Charles Ellicott Commentary Genesis 15:18

"In that day Jehovah made a covenant with Abram, saying, Unto thy seed have I given this land, from the river of Egypt unto the great river, the river Euphrates:" — Genesis 15:18 (ASV)

The Lord made a covenant. — Hebrew: Jehovah cut a covenant. Abram had divided the slaughtered animals, and Jehovah, by passing between them, made the whole act His own.

The river of Egypt. —That is, the Nile. In Hebrew, the Wady-el-Arish, on the southern border of Simeon, is always distinguished from the Nile, though this distinction is neglected in our version. Thus, in Numbers 34:5, Joshua 15:4, and Isaiah 27:12 (where, uniquely, an attempt is made at accuracy by translating it stream), the Hebrew has the torrent of Egypt, that is, a stream full after the rains but dry during the rest of the year.

For a description of these torrent-beds, see Isaiah 57:5-6, where in Genesis 15:5 the word is translated valleys, and in Genesis 15:6 stream. The word used here signifies a river that flows constantly; and Abram’s posterity are to found a kingdom conterminous with the Nile and the Euphrates, that is, with Egypt and Babylonia. If these bounds are large and vague, we must also remember that they are limited by the names of the ten nations which follow. Between the Nile and the Euphrates, only the territories of these ten tribes are definitely bestowed upon Abram.