One on horseback. — Literally, the rider of the horse.
What hast thou to do with peace? — A rough evasion: “What business is it of yours, on what ground I am come?” Conscious of his strength, Jehu can despise the royal message, and the messenger durst not disobey the fierce general, when ordered summarily to the rear. Of course Jehu wished to prevent an alarm being raised in Jezreel.
Came to them. — Literally, came right up to them. (The Hebrew text should be corrected from 2 Kings 9:20.)