'Keep' in the Bible

For the lips of the priest should guard and preserve knowledge [of My law], and the people should seek instruction from his mouth; for he is the messenger of the Lord of hosts.

“For I hate divorce,” says the Lord, the God of Israel, “and him who covers his garment with wrong and violence,” says the Lord of hosts. “Therefore keep watch on your spirit, so that you do not deal treacherously [with your wife].”

You have said, ‘It is useless to serve God. What profit is it if we keep His ordinances, and walk around like mourners before the Lord of hosts?