John Gill Commentary 1 Samuel 18:16

"But all Israel and Judah loved David; for he went out and came in before them." — 1 Samuel 18:16 (ASV)

And all Israel and Judah loved David
The verb is singular, and denotes that everyone of them loved him in all the tribes of Israel, as well as in Judah his own tribe; in such general esteem was he, and so much had he got the hearts and affections of the people:

because he went out and came in before them ;
the people, as in (1 Samuel 18:13) ; so the Septuagint version, in which, according to the Vatican copy, the verses (1 Samuel 18:17–19) are wanting.