Genesis 15:7 Meaning

5And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be.

6And he believed in the LORD; and he counted it to him for righteousness.

7And he said unto him, I am the LORD that brought thee out of Ur of the Chaldees, to give thee this land to inherit it.

8And he said, Lord GOD, whereby shall I know that I shall inherit it?

9And he said unto him, Take me an heifer of three years old, and a she goat of three years old, and a ram of three years old, and a turtledove, and a young pigeon.