Why is God merciful to Jacob?

The reader of the life of Jacob might be perplexed at this point. In no episode throughout the life of Jacob does he ever emerge as the hero. He has never behaved as a moral paragon; instead he continually acted in foolish, devious, or even vicious ways. He didn’t seem to deserve any blessing from God at all. Why, if God is holy and just, was He so gracious to Jacob? Why would God feign weakness to keep from killing him? Then give him clues as to who He was, then bless him for no better reason than that he held on desperately?
The answer to our question comes later in the Bible, when the Lord again appeared as a man. In the darkness with Jacob, God feigned weakness in order to save Jacob’s life. But in the darkness of Calvary, the Lord appeared as a man and became truly weak to save us. Jacob held on in obedience at the risk of his life, in order to gain blessing for himself. But when facing the Cross, though He could have turned aside, Jesus held on at the cost of His life, in order to gain the blessing, not for Himself, but for us.
 

Tim Keller, Counterfeit Gods, Dutton, 2009, pg. 162

First Washing, Then Worship

Through Him then let us continually offer up a sacrifice of praise to God, that is, the fruit of lips that acknowledge His name. - Hebrews 13:15

The words translated “sacrifice of praise” occur in the LXX of Leviticus 7:12 and speak of the highest form of peace offering under the old covenant. This thank offering was  voluntary offering and could only be made after the expiatory offerings had been presented and the worshiper was ritually clean; it’s primary purpose was to express gratitude to God.


George Guthrie, Hebrews NIV Application commentary, Zondervan 1998, page 449