John Gill 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] with the house of David Not with David himself only, which was now renewed, but with his family also:

[saying], let the Lord even require [it] at the hand of David's enemies ; take vengeance on Jonathan, or on any of his posterity, should they break this covenant, by showing themselves enemies to David, and his crown; and, on the other hand, also on David, and his posterity, should they not show kindness to Jonathan and his seed, according to the tenor of this covenant.