'Serving' in the Bible

Now Eli was very old, and he had heard everything that his sons were doing to the Israelis, and how they lay with the women who were serving regularly at the entrance to the Tent of Meeting.

Any of you whom I don't eliminate from serving at my altar will grow tired from weeping, and their souls will grieve. All the increase of your family will die by violence.

Meanwhile the boy Samuel was serving the LORD before Eli. A word from the LORD was rare in those days, and visions were infrequent.