The whole nation of Israel foolishly vowed to keep God’s commands. Christians should realise the utter stupidity of such a vow. It is the very reason why the New Covenant has FOREVER replaced the Old Covenant.

Jos 24:19 But Joshua said to the people, “You cannot serve the LORD, for He is a holy God. He is a jealous God; He will not forgive your transgressions nor your sins.
Jos 24:20 If you forsake the LORD and serve foreign gods, then He will turn and do you harm and consume you, after He has done you good.”
Jos 24:21 And the people said to Joshua, “No, but we will serve the LORD!”
Jos 24:22 So Joshua said to the people, “You are witnesses against yourselves that you have chosen the LORD for yourselves, to serve Him.” And they said, “We are witnesses!”
Jos 24:23 “Now therefore,” he said, “put away the foreign gods which are among you, and incline your heart to the LORD God of Israel.”
Jos 24:24 And the people said to Joshua, “The LORD our God we will serve, and His voice we will obey!”

yeah yeah obey His voice, serve the Lord…oh yeah, so holy of you…puke, vomit!!

God has forgiven all vows made under the old Covenant through the sacrifice of Jesus. But if we do not trust that sacrifice for all righteousness before God, then we shall continue to receive the curse of the law.
If we keep vowing and promising to not sin, promising to obey, we only reap curses…we make ourselves an enemy of the cross.
The new covenant is nothing to do with our vow to be a good Christian…NOTHING.