What does Genesis 28:21 mean?

In a dream, the Lord has appeared to Jacob and promised to be with him and bring him back to the land of promise. Now awake, Jacob is responding to that promise. If the Lord will really be with him, and keep me safe, and provide food and clothing, and, bring him back to his father's household in peace, then the Lord will be his God.

When we think of Jacob's situation, his emphasis on these things makes sense. Jacob was literally running away from his home to spare his life from his brother's fury (Genesis 27:41). He is apparently alone in the wilderness, traveling to find a wife among his mother's relatives (Genesis 28:1–2). Before this visit from the Lord, his future was murky and his path was dangerous. Now, because of God, Jacob has hope that he will be provided for, kept safe, and be able to return home.

It is interesting to note that God has already promised Jacob that He will be with him. The Lord has already made Jacob His man. Jacob doesn't declare the Lord to be his God in hopes that the Lord will take care of him. Jacob makes that declaration in response to God's promises and care. His worship and commitment follows God's gifts of grace, just as our does (Ephesians 2:8–10).