'A sandal tree' signifies aspects of the natural self.

(References: Apocalypse Explained 518)

293. The Lord came into the world to save the human race, which otherwise would have suffered eternal death. He saved it by gaining control over the hells, which were assaulting everyone who entered this world and everyone who left it. He also saved the human race by glorifying his own human nature, because this gave him the power to keep the hells under his control forever.

His gaining control over the hells and the simultaneous glorification of his human nature were effected by allowing the human nature that he received from his mother to undergo spiritual crises and by continuous victories in those crises. His suffering on the cross was his last spiritual crisis; in it he made his victory complete.