Often times, you will hear Christians say that the reason that people go to hell is because they failed to believe that Jesus is the Messiah and the One true Lord and Savior. However, if we examine the scriptures carefully, we will see that this is just not the case. I know this statement may seem a little confusing at first glance, but let's unpack this notion carefully.
It is safe for all who are Christians to affirm and proclaim that if you don't believe in the person and work of Jesus Christ that you will go to Hell. What is not safe to affirm or proclaim is that this is the reason that you are going to Hell in the first place (which is the implication that the statement seems to lend itself). We must remember that Jesus' life and death were sacrificial, not damning. Jesus died to bring us to God, not to further solidify our condemnation. I think that one of the problems for the confusion is that we have a strong tendency to read John 3:16 and then stop there, never paying attention to how Jesus explains the implications of it in the verses that follow (John 3:17-18). People end up in Hell, not because the don't believe in Jesus (first and foremost), but because they are in fact sinners deserving of punishment. When a person rejects Christ as the Messiah and the salvation of their soul, it simply shows that God is just in his judgement in sending anyone to hell, due to their hostility toward him (John 3:19-20, Romans 8:7).
This may just all sound like an exercise in mere semantics or hair-splitting, but it is much more than that. The implications on the way we do evangelism and view sin (both our own and that of others) run very deep. First of all, as far as evangelism is concerned, a misunderstanding of what Jesus actually accomplishes in life, death and resurrection will serve to diminish the threat of our already existing condemnation. In other words, people will never truly understand what they are being saved from. This ties right into the second point; since our condemnation doesn't proceed salvation under these implications (i.e. "God loves you, and has a wonderful plan for your life"), the need to accept Jesus will be diminished as well. After all, if you don't know that you're sick, why would you need a physician? This leaves wiggle room for us sinners to run to our "works". We are all rich young rulers at heart - ready to deceive ourselves into believing that we are good enough on our own. Therefore, accepting Christ becomes superfluous. This is where true danger lies; as we have seen in passages of scripture above, natural man will sooner leave it than take it.
We must remember that there is no good news without the bad news first. But, the bad news is not that unbelief will surely send you to Hell. The bad news is that we're going to Hell already (and rightfully so!). But a prodigal God has been gracious and has provided a substitute in his own son, and laid the punishment due squarely on his shoulders. All we must do is repent of our sins and believe in him who has paid the debt for us (Isaiah 53:5, Acts 17:30-31, Romans 5:12-21).
When you hear it put that way, why would you ever want to screw that up? It's our only hope...at the Cross is where we are forgiven, not condemned (John 12:31-33, Romans 3:21-26, 1 John 2:2; 4:10).
Soli Deo Gloria,