Adam Clarke on Genesis 31:48

I think these two verses are badly divided, and should be read thus: Gen 31:48 - And Laban said, This heap is a witness between me and thee this day. Gen 31:49 - Therefore was the name of it called Galeed and Mizpah; for he said, The Lord watch between me and thee, when we are absent one from another.

Mizpah - מעפה mitspah signifies a watch-tower; and Laban supposes that in consequence of the consecration of the place, and the covenant now solemnly made and ratified, that God would take possession of this heap, and stand on it as on a watch-tower, to prevent either of them from trenching on the conditions of their covenant.