John Calvin Commentary Romans 9:12

"it was said unto her, The elder shall serve the younger." — Romans 9:12 (ASV)

The elder shall serve the younger. See how the Lord makes a difference between the sons of Isaac, while they were still in their mother’s womb; for this was the heavenly answer, by which it appeared that God designed to show the younger peculiar favor, which He denied to the elder.

Though this indeed referred to the right of primogeniture, yet in this, as the symbol of something greater, the will of God was manifested.

We can easily perceive that this was the case when we consider what little benefit, according to the flesh, Jacob derived from his primogeniture.

For because of it, he was exposed to great danger. To avoid this danger, he was obliged to quit his home and his country, and was treated unkindly in his exile.

When he returned, he tremblingly, and in doubt for his life, prostrated himself at his brother's feet, humbly asked forgiveness for his offense, and lived through the indulgence shown to him.

Where was his dominion over his brother, from whom he was constrained to plead for his life? Therefore, there was something greater than the primogeniture promised in the answer given by the Lord.