John Gill Commentary Genesis 31:45

"And Jacob took a stone, and set it up for a pillar." — Genesis 31:45 (ASV)

And Jacob took a stone, and set it up [for] a pillar .
To show his readiness to agree to the motion, he immediately took a large stone that lay upon the mount, and set it up on one end, to be a standing monument or memorial of the agreement now about to be made between them.