Genesis 28:20

Lastly, Jacob made a vow: that if God would give him the promised protection on his journey, and bring him back in safety to his father's house, Jehovah should be his God (והיה in Gen 28:21 commences the apodosis), the stone which he had set up should be a house of God, and Jehovah should receive a tenth of all that He gave to him. It is to be noticed here, that Elohim is used in the protasis instead of Jehovah, as constituting the essence of the vow: if Jehovah, who had appeared to him, proved Himself to be God by fulfilling His promise, then he would acknowledge and worship Him as his God, by making the stone thus set up into a house of God, i.e., a place of sacrifice, and by tithing all his possessions. With regard to the fulfilment of this vow, we learn from Gen 35:7 that Jacob built an altar, and probably also dedicated the tenth to God, i.e., offered it to Jehovah; or, as some have supposed, applied it partly to the erection and preservation of the altar, and partly to burnt and thank-offerings combined with sacrificial meals, according to the analogy of Deu 14:28-29 (cf. Gen 31:54; Gen 46:1).

We have here, I. Jacob parting with his parents, to go to Padanaram; the charge his father gave him (Gen 28:1, Gen 28:2), the blessing he sent him away with (Gen 28:3, Gen 28:4), his obedience to the orders given him (Gen 28:5, Gen 28:10), and the influence this had upon Esau (Gen 28:6-9). II. Jacob meeting with God, and his communion with him by the way. And there, 1. his vision of the ladder (Gen 28:11, Gen 28:12). 2. The gracious promises God made him (Gen 28:13-15). 3. The impression this made upon him (Gen 28:16-19). 4. The vow he made to God, upon this occasion (Gen 28:20, etc.).

28:20-22 In view of what God would do for him, Jacob vowed to do certain things for God. He believed the Lord’s words and responded in gratitude. Jacob’s vow influenced Israel’s way of making commitments to God in worship.