God keeps the promise he made with Abraham by allowing Rebekah (his daughter-in-law) to give birth to Esau and Jacob. God is faithful with his promise.
Again pay attention to “I will” of God (e.g., vv. 3 and 4). Yahweh keeps his covenant due to Abrahamic Covenant (v. 24), which further demonstrates his faithfulness to his promise.
What happens here with Jacob and Esau gets explained later in Romans 9. Even though Jacob uses deceptions against Esau, as Romans 9 implies it was part of God’s sovereign purpose. That is, God allows or uses providence to work out his sovereign plans/purposes in the lives of his people (even people outside of his covenantal community) to accomplish greater picture/plans.
Yahweh created or allowed situation which prompted Jacob to leave and arrive at a place God ordained. God assures his covenant to Jacob via dream. The point is God assures and demonstrates that he and his promises can be trusted.
Like many saints who have experienced doubts in early years, Jacob “bargains” with Yahweh, namely his “if, then” conditional contract (vv. 20-21). He vows at the end to give “a tenth” to Yahweh if Yahweh really comes through at the end. The notion of giving tenth is introduced by Jacob (v. 22).