In and of himself the natural man has power to reject Christ; but in and of himself he has not the power to receive Christ. And why? Because he has a mind that is "enmity against" Him (Rom. 8:7); because he has a heart that hates Him (John 15:18). Man chooses that which is according to his nature, and therefore before he will ever choose or prefer that which is Divine and spiritual a new nature must be imparted to him; in other words, he must be born again.

The Sovereignty of God, by A. W. Pink