Charles Ellicott Commentary 2 Samuel 19:7

"Now therefore arise, go forth, and speak comfortably unto thy servants; for I swear by Jehovah, if thou go not forth, there will not tarry a man with thee this night: and that will be worse unto thee than all the evil that hath befallen thee from thy youth until now." — 2 Samuel 19:7 (ASV)

I swear by the Lord. —The statement which Joab emphasizes with this solemn oath is not that he will lead the people into revolt—he does not seem to have conceived, far less to have expressed any such design—but it is simply an assurance of the extreme danger of the course David was pursuing, put in such a strong and startling way as to rouse him from the selfishness of his sorrow.