John Wesley on Genesis 28:18

He set up the stone for a pillar - To mark the place again, if he came back, and erect a lasting monument of God's favour to him: and because he had not time now to build an altar here, as Abraham did in the places where God appeared to him, Gen 12:7, he therefore poured oil on the top of this stone, which probably was the ceremony then used in dedicating their altars, as an earnest of his building an altar when he should have conveniencies for it, as afterwards he did, in gratitude to God, Ge 35:7. Grants of mercy call for our returns of duty and the sweet communion we have with God ought ever to be remembered.