The Abraham narrative of Genesis begins with a promise of land and descendants like the sand and stars.
It ends with a down payment on the promise. Abraham sojourns in the land, but after Sarah dies he negotiates the purchase of a burial site (Genesis 23). It is the only piece of property he owns in the land that is promised to his seed.
Then he remarries, and his second wife Keturah bears him six suns (25:1-2). It is a down payment on a seed like the dust of the earth, a pledge that Yahweh will do as He promised.