Why is it so important to know that Abner had gone in peace?
2 Samuel 3:22–23 (ESV)
22Just then the servants of David arrived with Joab from a raid, bringing much spoil with them. But Abner was not with David at Hebron, for he had sent him away, and he had gone in peace.
The fact that Abner had left Hebron in peace is highlighted. This is done to emphasize that there was a new relationship between him and David, that he was a friend and not an enemy.
22 Just then the servants of David arrived with Joab from a raid, bringing much spoil with them. But Abner was not with David at Hebron, for he had sent him away, and he had gone in peace.