Yahweh shows Abram the starry heavens and says “so shall your seed be.” Abram believes, and Yahweh counts it as righteousness (Genesis 15).
When Paul quotes this in Galatians, he emphasizes the singleness of that Seed: The Seed is Christ.Paul claims that the seed promised to Abram is fulfilled in Christ.
That seed may be the individual Jesus or, as N.T. Wright has argued, the corporate Christ. Either way, the seed is a starry seed, either Jesus the heavenly man or the church as the constellations and galaxies of the highest heavens. Either way, Yahweh promised a seed that is light in the darkness, a seed royal like the stars of heaven.