'Observe' in the Bible

For circumcision benefits you if you observe the law, but if you are a lawbreaker, your circumcision has become uncircumcision.

but I observe another law in my members, at war with the law of my mind and making me captive to the law of sin that exists in my members.

But if we hope for what we do not yet observe, we eagerly wait for it with patience.

He who observes the day, observes it to the Lord; and he who does not observe the day, to the Lord he does not observe it. He who eats, eats to the Lord, for he gives God thanks. He who doesn't eat, to the Lord he doesn't eat, and gives God thanks.