I have always understood Gen 28:20-22 as a simple expression of Jacob's acceptance of the divine covenant made with Abraham (Gen 12:1-3, Gen 15, Gen 17, Gen 18:9-15) which was inherited and then reconfirmed to both Isaac and Jacob.  We are told this numerous times in places like:
 - Ex 2:24 - So God heard their groaning, and He remembered His **covenant** with Abraham, Isaac, and **Jacob**.
 - Deut 9:5 - It is not because of your righteousness or uprightness of heart that you are going in to possess their land, but it is because of their wickedness that the LORD your God is driving out these nations before you, to **keep the promise** He swore to your fathers, to Abraham, Isaac, and **Jacob**.
 - Deut 29:13 - and so that He may establish you today as His people, and He may **be your God as He promised** you and as He swore to your fathers, to Abraham, Isaac, and **Jacob**.
 - 2 Kings 13:23 - But the LORD was gracious to Israel and had compassion on them, and He turned toward them because of His **covenant** with Abraham, Isaac, and **Jacob**. And to this day, the LORD has been unwilling to destroy them or cast them from His presence.
 - 1 Chron 16:17 - He confirmed it to **Jacob** as a decree, to **Israel** as an everlasting **covenant**:
 - etc

Thus, Jacob, at this point (gen 28) decided to abide by the covenant requirements and accept the covenant advantages and promises.