Show me unfailing kindness like the Lord’s kindness as long as I live

1 Samuel 20:1-24
Then David fled from Naioth at Ramah and went to Jonathan and asked, “What have I done? What is my crime? How have I wronged your father, that he is trying to kill me?”
Then Jonathan said to David, “I swear by the Lord, the God of Israel, that I will surely sound out my father by this time the day after tomorrow! But show me unfailing kindness like the Lord’s kindness as long as I live, so that I may not be killed, and do not ever cut off your kindness from my family—not even when the Lord has cut off every one of David’s enemies from the face of the earth.
And Jonathan had David reaffirm his oath out of love for him, because he loved him as he loved himself.
And about the matter you and I discussed—remember, the Lord is witness between you and me forever.”
Jonathan tries to secure David's safe return, but his father turns on him.
Why?
David fled and met Janathon in the field, they make an oath for they love each other.
The Lord is the witness between David and Jonathan.
Jonathan knew David will be a king of Israel in the future, so he asked David to protect his family and show his kindness.
Show me unfailing kindness like the Lord’s kindness as long as I live. This is an oath between David and Jonathan. 
How?
An oath made before the Lord is a serious matter, so do not make an oath but say the truth.