'Service' in the Bible

Warfare was severe against [the] Philistines all the days of Saul. Whenever Saul saw {anyone who was a mighty warrior} or {any brave man}, he {conscripted him into his service}.

So David came to Saul and {entered his service}. He loved him greatly and {he became Saul's armor bearer}.

So Jonathan spoke well about David to his father Saul and said to him, "The king should not sin against his servant David, because he has not sinned against you, and because his service for you [has been] very good.

Then David said to Achish, "But what have I done? And what have you found in your servant from the day that I {entered your service} until this day, that I should not go and fight against the enemies of my lord the king?"