God, who is infinite love and mercy, is also infinite justice. Because of God's justice as well as his total respoect for human freedom, hell is a real possibility as a person's eternal destiny. This side of God's mystery is difficult for us to grasp. But Christ himself taught it, and so does the Church.
The teaching on hell is clearly in Scripture. In the Gospel of Matthew, Christ says to the just," Come, O blessed of my Father, inherit the kingdom prepared for you from the foundation of the world." But to the unjust he says," Depart from me, you cursed, into the eternal fire prepared for the devil and his angels" (Mt 25:34,41) Elsewhere Jesus is recorded as saying,"It is better for you to enter life maimed than with two hands to go to hell, to the unquenchable fire" (Mk 9:43)
One point that emerges quite clearly from this doctrine is the reality of human freedom. You are free to seek God and serve him. And you are free todo the opposite. In either case, you are responsible for the consequences. Life is a serious matter. The way you live it makes a serious difference. You are free, radically free, to seek God. And you are free, radically free, to choose the inexpressible pain of his absence.