Saul’s oath was meant to convince Jonathan that Saul's plans to take David’s life had come to an end. This would be the fourth oath that Saul made (see 1 Samuel 14:1–52), a legitimate oath which he would break to incur God’s wrath (see Deuteronomy 23:21–23).
6 Saül écouta la voix de Jonathan, et il jura, disant: L'Eternel est vivant! David ne mourra pas.