mishmeret

This is the most common use of the word, and it comes straight from the verb behind it, which means to keep, watch over, or guard. A charge is something handed to you to look after: an assignment you are responsible for and answerable for. The phrase that runs through the law is to keep the charge of the LORD, or the charge of the tabernacle, meaning to carry out the service God has assigned and to make sure it is not neglected.

Most often the charge belongs to the priests and Levites. Their charge was the upkeep, protection, and right handling of the sanctuary and its worship, a sacred trust that could not be left undone or done carelessly. Because the duty was real and ongoing, the word easily widens to cover any solemn obligation a person is bound to keep, as when God says Abraham kept my charge along with my commandments.

When the priestly service was organized into rotating shifts, the same word came to name a division or course of men assigned to a turn of duty. The idea is unchanged: a charge is still a charge, now spread across teams who take it in turns.

Here the word keeps the guarding side of the verb in a more literal sense. A watch is the act and the station of standing guard, the duty a sentry holds at his post. To stand on your watch is to be at your assigned place, alert and on duty, as the prophet pictures himself waiting for God to answer.

From the duty the word reaches to the people who perform it. After the wall of Jerusalem was rebuilt, watches were appointed: bodies of men posted to guard the gates and the temple. So the word can name the guard duty itself or the company of guards who keep it. A close relative of this idea is being held in someone's keeping, whether for protection or for confinement.

When the thing kept is a physical object rather than a task, the word names what is laid up for safekeeping. Something held for a watch is something stored, set aside, and guarded until the time it is needed or as a lasting reminder.

This is the sense in the wilderness accounts: the Passover lamb is kept until the appointed day, a jar of manna is laid up before the LORD for the generations to come, and Aaron's rod and the ashes of the red heifer are preserved as enduring signs. In each case the word marks not a duty to perform but a thing carefully kept.