”Looking diligently lest any man fail of the grace of God; lest any root of bitterness springing up trouble you, and thereby many be defiled; Lest there be any fornicator, or profane person, as Esau, who for one morsel of meat sold his birthright. For ye know that afterward, when he would have inherited the blessing, he was rejected: for he found no place of repentance, though he sought it carefully with tears.” –Hebrews 12:15-17
One of the hardest truths of Christianity to grasp is the teaching that there is a point of rejecting the will of God beyond which a man may never find repentance. Sin hardens the heart toward the things of God. When we are young, our hearts are tender, which explains in part why so many believers today came to Christ as children. As people progress through life without responding to God, His voice grows steadily silent to their souls. Eventually, through the deceitfulness of sin, their hearts are seared over and they will never repent.