'Observance' in the Bible

It is a night of observance to Jehovah, because of their being brought out from the land of Egypt: that same night is an observance to Jehovah for all the children of Israel in their generations.

and he told them, "This is what the LORD said: "Tomorrow is a Sabbath observance, a holy Sabbath to the LORD. Bake what you want to bake and boil what you want to boil, and put aside whatever remains to be kept for yourselves until morning.'"

The Israelis are to keep the Sabbath to make the Sabbath observance a perpetual covenant from generation to generation.

and so cause them [by neglect of any essential observance] to bear the punishment of guilt when they eat their holy things; for I am the Lord who sanctifies them.’”

Now Ezra had dedicated himself to the study of the law of the Lord, to its observance, and to teaching its statutes and judgments in Israel.