Keep the watch of the Lord - i. e. guard against any attempt that might be made by the Baal-worshippers to force their way through the courts into the temple.
Related Commentaries of 2 Chronicles 23:6
2 Chronicles 23:6
6 But let none come into the house of the LORD, save the priests, and they that minister of the Levites; they shall go in, for they are holy: but all the people shall keep the watch of the LORD.