In your opinion what causes christians to believe in Jesus

[Sheldon]

I think you're talking about works, more properly.  Faith is a mental attitude which can be expected, or maybe should be expected, to result in acts.  

faith becomes meaningless if God doesn't exist, in much the same way that trusting your spouse is meaningless if your spouse doesn't exist. 

Another false equivalence, since it is an objective fact a spouse exists / is possible, as it is an objective fact a spouse may behave in a way that deserves your trust, unlike a deity, or deities, as no one can objectively demonstrate they exist or are possible, and therefore deserving of (religious) faith. 

God....He has to exist before you can have faith in him.

An absurdly circular argument, and it is demonstrably false to claim a belief must be true, before someone can hold that belief.