"Then Jacob made a vow, saying, 'If God will be with me and will watch over me on this journey I am taking and will give me food to eat and clothes to wear so that I return safely to my father's household, then the Lord will be my God and this stone that I have set up as a pillar will be God's house, and of all that you give me I will give you a tenth." NIV translation
When you first read this passage, it may seem like it is all good and that Jacob has had a breakthrough in his faith but a closer look reveals the magnitude of his mistake. We remember that, in Jacob's dream, God made promises to him to do all of the things that are listed here.
Here, we see that Jacob turned those promises into a contract. Instead of accepting the things that God said and being grateful for them, Jacob promised to recognize God if God kept up His side of the deal. He was either not sure of God's ability to keep His promises or not sure of God's character and the fact that He cannot break His promises. This type of a contract is at the heart of all religion and is the opposite of faith. We are reminded that it is only through our faith (trust) in God that we can please Him.
We have the assurance of everlasting life as well as the promise that God will provide for us in this world but it is not through a contract or religion. We have His promises because we trust in Jesus and His character not because of anything that we can do to please Him.
Jacob did not have the information that we have concerning what God has done so we can understand why he would try to make this contract. On the other hand, we have all of the information that we need to know as well as the Holy Spirit living in us so there is no excuse for trying to turn God's grace into a religion.