Thomas Boston, Works, 6:115:
God hath so ordered the matter of the believer’s sanctification, that sin is left to be active in their souls while here, for their further humiliation. They are hereby taught to bear low sails all the days of their lives, and, with “Hezekiah, to go softly all their years in the bitterness of their souls” (Isa. 38:15). Wherefore we read (2 Cor. 12:7), that lest Paul should be exalted above measure through the abundance of revelations, there was given to him a thorn in the flesh, a messenger of Satan is sent to buffet him. And so we find David (Ps. 51), after his grievous fall, grows in the grace of humility.
God hath so ordered the matter of the believer’s sanctification, that sin is left to be active in their souls while here, for their further humiliation. They are hereby taught to bear low sails all the days of their lives, and, with “Hezekiah, to go softly all their years in the bitterness of their souls” (Isa. 38:15). Wherefore we read (2 Cor. 12:7), that lest Paul should be exalted above measure through the abundance of revelations, there was given to him a thorn in the flesh, a messenger of Satan is sent to buffet him. And so we find David (Ps. 51), after his grievous fall, grows in the grace of humility.