In your opinion what causes christians to believe in Jesus

[Angrboda]

Some willful ignorance, a bit of wishful thinking, and a metric shit ton of fear of death.

The average person doesn't go around thinking of death, much less fearing it, until its right at their doorsteps. And if they fear anything about it, it is the process and manner of dying rather than the state of being dead itself that worries people.

The most that Christianity offers is an explanation for why death occurs, but it does not do anything to prevent it or make it more palatable. After all, the most significant symbol in Christianity is that of a dead man hung on a cross—not exactly the most marketable imagery.

If there is no afterlife, there is no point to Christianity. I wouldn't say it is the only or maion thing, but without it, few people would bother to believe.