Exodus 4:21

In thine hand, i.e. in thy power or commission, to be clone by thy hand, and the rod in it. I will harden his heart, that he shall he unmerciful to all the groans and pressures of the Israelites, inexorable to the requests of Moses, unmovable and incorrigible by all my words and works. But God doth not properly and positively make men's hearts hard, but only privatively, either by denying to them, or withdrawing from them, that grace which alone can make men soft, and flexible, and pliable to the Divine will; as the sun hardens the clay by drawing out of it that moisture which made it soft; or by exposing them to those temptations of the world or the devil, which, meeting with a corrupt heart, are apt to harden it.