Albert Barnes Commentary 2 Samuel 15:20

"Whereas thou camest but yesterday, should I this day make thee go up and down with us, seeing I go whither I may? return thou, and take back thy brethren; mercy and truth be with thee." — 2 Samuel 15:20 (ASV)

Thou camest but yesterday - Meaning, “You are not a native Israelite, but only a sojourner for a few years; therefore, there is no reason for you to share my calamities. Return to your place, your adopted home Jerusalem, and to the king, Absalom” (2 Samuel 15:34–35).