'Guard' in the Bible

Did he not make them one? And the vestige of the spirit remains in him. And why did he make them one? He was seeking godly offspring. So guard yourselves in your spirit, and don't be unfaithful to the wife of your youth.

"Indeed, the LORD God of Israel says that he hates divorce, along with the one who conceals his violence by outward appearances," says the LORD of the Heavenly Armies. "So guard yourselves carefully, and don't be unfaithful."