Sworn friendship with each other in the name of the Lord

1 Samuel 20:24-42
As long as the son of Jesse lives on this earth, neither you nor your kingdom will be established. Now send someone to bring him to me, for he must die!
 “Why should he be put to death? What has he done?” Jonathan asked his father. But Saul hurled his spear at him to kill him. Then Jonathan knew that his father intended to kill David.
Jonathan said to David, “Go in peace, for we have sworn friendship with each other in the name of the Lord, saying, ‘The Lord is witness between you and me, and between your descendants and my descendants forever.’” Then David left, and Jonathan went back to the town.
Jonathan tries to secure David's sage return, but his father turns on him, and the two friends are forced to part.
Why?
Saul afraid David for if he lives his kingdom would not be established. So Jonathan knew his father really want to kill David.
Jonathan and David have an oath before the Lord, and Jonathan knew David will be king of Israel, so he asked David to bless his descendants. And David did his promise to Jonathan.
Jonathan let David fled from the dangerous place, escaped to save place so David appreciated Jonathan let him know this situation.
Friendship is helping friends from a dangerous situation. 
How?
The relationship is person to person, and should not relate to his family. As if our salvation from the Lord is a personal relationship.