When they came to the land of Canaan, Abram passed through the land to the place at Shechem, to the oak of Moreh. At that time the Canaanites were in the land. Then the LORD appeared to Abram and said, “To your Seed I will give this land.” So he built there an altar to the LORD, who had appeared to him.

So the promise was made.  IN YOU – your offspring in you— because of your seed all the earth will be blessed.

He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ.

HOW IS THIS POSSIBLE?