'Observe' in the Bible

Nobody is to enter the LORD's Temple except for the priests and descendants of Levi who are on duty. They may enter because they are ceremonially holy, but all the rest of the people must observe the LORD's instructions.

Hezekiah also sent word to all of Israel and Judah, and wrote letters to Ephraim and Manasseh that they should come to the LORD's Temple in Jerusalem to observe the Passover to the LORD God of Israel.

The king, his princes, and the entire assembly in Jerusalem had mutually decided to observe the Passover in the second month,

Many of the people gathered together in Jerusalem to observe the Festival of Unleavened Bread during the second month. It was a very large assembly.