The crucifixion of Christ makes no sense

This has been something I've been thinking about so bear with me. If Jesus existed and he truly died on the cross for our sins, why does it matter if we believe in him or not. If his crucifixion actually happened, then why does our faith in him determine what happens to us in the afterlife? If we die and go to hell because we don't believe in him and his sacrifice, then that means that he died in vain.