Westminster Confession 5:6
6. As for those wicked and ungodly men whom God, as a righteous judge, blinds and hardens because of their past sins, God withholds his grace, by which their minds might have been enlightened and their hearts affected. He also sometimes takes away the gifts which they had, and exposes them to such things as their corrupt nature makes into occasions for sinning. Moreover, he gives them over to their own lusts, the temptations of the world, and the power of Satan, by which they harden themselves even under the same means which God uses to soften others.
God, in His providence toward willingly evil men, sometimes withholds his restraining grace and so blinds and hardens them in their sins. He does this due to their past sins. Don’t miss that. God is responding here to pre-existing sin. It is the beginning of their just punishment for their selfish rebellion against him. If a sign says do not touch this wall. And a wicked man not only touches it, but leans his whole weight upon it. If that wall is suddenly taken away and the man falls, whose fault is it? God restrains sin; He keeps the evil heart of man from destroying everything. If He removes the walls that restrain the sinful desires of man so that they sink deeper into sin, whose fault is it? “He gives them over to their own lusts.” God takes away from sinners, the gifts that he had at first given to them.
“The same sun which melts wax hardens clay. And the same Gospel which melts some persons to repentance hardens others in their sins,” preached C.H. Spurgeon. The preaching of the gospel melts the hearts of some, but hardens the hearts of others. They harden themselves to its heart softening message.