WPNT(i)
7 Neither are they all ‘children’ because they are Abraham’s descendants; but, “in Isaac will your seed be called”.
8 That is, it is not the physical children who are God’s ‘children’, but the children of the promise are regarded as ‘seed’.
9 For this is the word of promise: “At this season I will come, and Sarah will have a son.”
10 Not only that, but also when Rebecca had conceived twins by our forefather Isaac
11 (though they had not yet been born, not having done anything good or bad, so that God’s purpose according to election might stand, not of works but of Him who calls),
12 it was said to her, “The older will serve the younger”.
13 As it is written: “Jacob I loved, but Esau I hated.”
14 So what shall we say, there is no injustice with God, is there? Of course not!
15 For He says to Moses: “I will have mercy on whomever I have mercy, and I will have compassion on whomever I have compassion.”
16 So then, it is not of him who wills nor of him who strives, but of God who shows mercy.