Charles Ellicott Commentary 1 Samuel 20:16

"So Jonathan made a covenant with the house of David, [saying], And Jehovah will require it at the hand of David`s enemies." — 1 Samuel 20:16 (ASV)

So Jonathan made a covenant. —It is not necessary to supply (as in the English Version) “saying,” but it is better to understand this verse as a remark interposed in the dialogue by the narrator, and to translate the Hebrew literally, So Jonathan made a covenant with the house of David, and Jehovah required it from David’s enemies.