Clue: Son of David rating peace for Israel — that's not hard (7)
Answer: ABSALOM
Explanation: Definition: Son of David
 AB(abbrev. for "able-bodied seaman"/a seaman or naval rating) + "shalom!"("Peace!", as a greeting among the Jewish people of Israel) **minus**(that's not) "h"(abbrev. for "hard").
Defn: … in the Bible.