What does 1 Samuel 7:15 mean?

Samuel was the last of the judges of Israel. As with the previous judges, God raised Samuel up as a deliverer to lead the people to victory over their oppressors after they had repented from their sins against Him (Judges 2:11–23). One of Samuel's jobs as judge and prophet would be to lead Israel through the transition from the time of judges to the time of kings. As this verse notes, that calling from God was permanent: once called, Samuel spent the rest of his days serving in this capacity.

It's hard to imagine a life better spent than fulfilling one's calling in serving the Lord from the very beginning (1 Samuel 1:27–28) to the very end (1 Samuel 25:1).