We might think that talking about the afterlife (the joys of heaven, the terror of hell) is a ploy to get you into 'religion' and it's certainly a common tactic seen in pseudo-Christian as well as other worldviews. Buddism/Hinduism has karma and reincarnation. In Islam you have to earn your way to heaven. Most ancient religions honour the dead. Only an Atheist belief keeps you away from that - but it offers no comfort in its place. Most people find it takes more faith to believe in nothing than to just accept that there is something. This 'numinous' sense is seen as part of God's providence - as with conscience - providing a starting point for people.
By Grace
In Christianity, some claim that all will go to heaven - Universalism - but there is little Biblical evidence to back this up other than the appropriation of God's expressed love in a diffuse sense. This originates from the idea that we're all nice people really, and all those bad attributes will disappear when we get to heaven.
Instead, it shows a massive misunderstanding, we deserve to be excluded. If this were not the case God would not have to give his Son to buy us back - which is the absolute basis and foundation of Christianity.
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.
It is God's love that takes seriously everything from murder to child abuse to pride - and deals with it. We can't save ourselves or ever be 'good enough' - even though justifying ourselves is a constant mental activity!
For it is by grace you have been saved, through faith – and this is not from yourselves, it is the gift of God – not by works, so that no one can boast.
When we die - 'that will not be the time for choosing: it will be the time when we discover which side we really have chosen, whether we realised it before or not. Now, today, this moment, is our chance to choose the right side. God is holding back to give us that chance. It will not last forever. We must take it or leave it.' CS Lewis, The Case for Christianity
The essence of sin is man substituting himself for God, while the essence of salvation is God substituting himself for man. John Stott, The Cross of Christ.
Eternal quality of life
This is not about 'fire and brimstone' preaching (though it could be). It is recognising the truth of the fallenness of our world - how far we are from God, and what God offers us. 'Eternal life' is not just living for ever, but the quality of life that would be capable of that. God shows us more of the bad in ourselves as he shows how we are rescued from it. People who catch this truth want to share it.
'The Doctrine of Grace combined with the Doctrine of Hell fueled the growth of the early church. It fueled the Great Awakenings. It fueled global missions. It served to restrain evil even among those whose belief in God did not extend to an actual conversion.’ Larry Taunton
Seriously
We have to take him seriously - about Aslan: '"Safe?" said Mr Beaver ..."Who said anything about safe? Course he isn't safe. But he's good. He's the King, I tell you.”' C.S. Lewis, The Lion, the Witch and the Wardrobe
'The Lord God Almighty lives, and he is not to be trifled with. And whether you take him seriously or not does not alter an inescapable fact: He is coming for you. It will come suddenly, and unexpectedly.'
2 Peter 3:10 says, “The Day of the Lord will come like a thief …” On that Day, you will hear him say one of two things: “Come, you who are blessed by my Father, inherit the kingdom prepared for you from the foundation of the world.” Or … “Depart from me, you cursed, into the eternal fire prepared for the devil and his angels.” (Mt 24: 34, 41 )
Pass it on.
R.C. Sproul: What happens when you wake up in Hell? pic.twitter.com/daTsl7u38g— Justin Bullington (@JustnBullington) November 23, 2022
New Heaven, New Earth
We also have to show that we actually want 'heaven' - do we want to be with him - do we love him and his ways? Can we say like David
Lord, I love the house where you live, the place where your glory dwells.
We do not have a comprehensive picture of heaven, probably because there are vast parts of it beyond our understanding, but God has given us a foretaste of it on earth. There are many echoes of Eden glory still present - from delight in nature and beautiful things to the satisfaction of creativity and work, the warmth of friends and love of family and essentially in our relationship with him through the Spirit.
We know there will be a New Earth as well, which underlines the intrinsic value of the created material world - that God declared was created 'very good'.
And you also were included in Christ when you heard the message of truth, the gospel of your salvation. When you believed, you were marked in him with a seal, the promised Holy Spirit
For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known.