One wonders, also, why Cain says what he does in this verse. Because, after mentioning that he would be driven “from the face of the Earth,” he states that he would be hidden from God’s face. Without knowing exactly what was on Cain’s mind, it appears that he wasn’t ready to receive forgiveness. In Psalm 51:11, David pleads for God not to hide His face from him, but to forgive him instead.
It’s possible, of course, that Cain doesn’t feel he can be forgiven. But, if that was the case, God surely would have approached it differently. Peter, for example, wept bitterly after denying the Lord. (Mat. 26:75) The Lord made special mention, however, after rising from the dead, that Peter should be told. He says “Go, tell My disciples, and Peter,” as if perhaps Peter wonders if he is fit to be a disciple anymore. (Mark 16:7) Mark had made a major mistake leaving the mission field once in Acts, and yet later, Paul wishes him to be brought, because Paul knows he will be of great help in the ministry. (2 Tim. 4:11) The Bible is filled with people who have had second chances, and made the most of them.
The most likely possibility is that Cain knew that God was not planning to accept his ways. And, that if that was the case, he knew God would hide his face from him. This, sadly, happens as well in Scripture, such as with King Saul. After the Holy Spirit leaves King Saul, he makes no effort to get right with God. He cares only about the kingdom that has been removed from him. In the same way, consumed with jealousy, Cain chose to destroy the one the Lord favored. Even thought turning back to God in repentance could at least restore his eternal soul.
It’s no wonder the Lord Jesus Christ makes such a major point, thousands of years later, when He tells the people to consider what it can profit a man to gain the whole world, and yet lose his immortal soul. There is no profit at all. And, it breaks God’s heart when someone won’t repent and turn to Him.