What does 1 Samuel 20:21 mean?

Then I’ll send a boy to find the arrows. If I say, Look, the arrows are on this side of you, bring them here, then you’re safe and can come out. As sure as the Lord lives, there’s no danger. 1 Samuel 20:21 - Modern Text Bible

(Jonathan explains the signal: if he tells the boy the arrows are close, it’s safe for David.)