One of the most common reasons people give as to why we should not speak about hell is this: "But people don't like to hear about hell?" They're not supposed to! Nobody likes hearing about being run over by a double-decker bus, but that doesn't stop us from warning people about the dangers of standing in the middle of a busy road. It's not an unloving thing to warn people of a real danger.
If we merely tell people what they like to hear then we are no different to the false teachers that Timothy had to deal with, who taught what people's "itching ears" wanted to hear (2 Timothy 4:3). Just because someone doesn't want to hear about something does not mean that they do not need to hear it.
We need to speak about hell. If we neglect this it gives us a wonky gospel. The reality of God's eternal judgement is part of the gospel. In Revelation 14:6 John sees an angel "with an eternal gospel to proclaim to those who dwell on earth, to every nation and tribe and language and people." What is the content of this eternal gospel? John tells us in verse 7, the angel proclaims: "Fear God and give him glory, because the hour of his judgement has come, and worship him who made heaven and earth, the sea and the springs of water."
Therefore, if we are to be faithful in proclaiming the gospel, and to avoid having a wonky gospel, we need to speak about God's judgement, which means speaking about hell. Hell is a real place where real people, who have not submitted to the Lord Jesus, shall spend eternity (see e.g. John 3:36, Revelation 20:11-15). This ought to grieve us and we ought to tremble over the thought of people facing such a future. Therefore, if we love people, instead of shying away from speaking about the reality of God's just judgement, we ought to speak of it with tears in our eyes urging them to flee to the Lord Jesus that they might have life.
In order to help us think through why we shouldn't neglect speaking about hell here are some initial thoughts on what happens to the gospel if we lose our doctrine of hell. What do we lose if we ignore hell?
1) We Lose a Just God
If there is ultimately no final judgement where people recieve the justice due to them for rebelling against an infinitely holy God, then this would mean that God is not just. It would mean that there is no hope that every wrong shall one day be righted.
2) We Lose the Seriousness of Sin
If God does not judge sin fully and finally then it implies that He doesn't really care about sin. This would then lead to us not really caring about sin. If God doesn't care enough about sin to punish it, why then should I care about seeking to live a godly life and turn from it. Yet, sin is infinitely serious. Dragging the glory of the eternal and infinitely holy God through the dirt, which is what we do when we sin, is of the utmost seriousness.
3) We Lose the Glory of God's Grace Displayed in the Cross
If there is no such thing as hell then we lose the ultimate display of the glory of the grace of God: the cross of Christ. If there was no such place as hell then what was the point of the cross? If God is not going to judge sin eternally then the cross was the biggest waste of time. But this is not true. God shall judge sin eternally, therefore the cross is infinitely glorious. At the cross God is showing that He is both just and the one who justifies sinful people, who have faith in Jesus (Romans 3:21-26). At the cross the one who shall be the judge on that final day (Acts 17:31), has taken upon Himself the full weight of the wrath of God in the place of His people. If we neglect to speak about hell then the glory of the cross, the blazing centre of the revelation of the glory of God, loses its lustre.