Hell is not temporary. It is a place of eternal punishment. Those sent there have no hope of escape, and, contrary to what some Christians believe, they are not annihilated once God has determined they have suffered sufficiently for their sins.
Revelation 20:10 says that the devil, the beast, and the false prophet will be thrown into the lake of fire where "they will be tormented day and night forever and ever." This is known as the "second death," something that has no power over believers (Revelation 20:6). "But as for the cowardly, the faithless, the detestable, as for murderers, the sexually immoral, sorcerers, idolaters, and all liars, their portion will be in the lake that burns with fire and sulfur, which is the second death" (Revelation 21:8). There is no indication that there will ever be an end to their suffering.
Does it make sense to condemn a finite sinner to an everlasting punishment? Wouldn't that make God unjust? Such questions fail to take into consideration all of God's attributes. Yes, he is love, but he is also just and holy and eternal. And considering that it took the death of an infinitely holy and eternal God to pay the price for sin so that we might be redeemed, it stands to reason that the only just penalty for sinning against that same infinitely holy and eternal God is an infinite and eternal punishment.
Let's not complicate the issue. The choice is clear: eternal death or eternal life. We talk about Hell not to scare people into the Kingdom but to emphasize just how seriously God takes sin.