John Gill Commentary 1 Samuel 20:23

"And as touching the matter which thou and I have spoken of, behold, Jehovah is between thee and me for ever." — 1 Samuel 20:23 (ASV)

And [as touching] the matter which you and I have spoken of The covenant they had made between them and their families:

behold, the Lord [be] between me and you for ever : as a witness of the covenant, and a revenger of those that should break it; so the Targum, ``behold, the Word of the Lord be between me and you a witness for ever.''