In your opinion what causes christians to believe in Jesus

[Sheldon]

The tricky bit about the free will debate is that the universe would look exactly the same whether or not free will exists. Let’s say you had eggs for breakfast. How could you possibly know if that was a free choice or if it was a necessary consequence of the universe unraveling in a particular way?

I think the absence of free will heavily implies complete capture by external stimuli. I would expect to see nothing but cascades of reflexive behavior from top to bottom. And what's telling here is that we do have such systems in limited quantities. In a typical reflex arc, if you grab a hot plate the sensory signal travels to the spinal cord and bounces back as a motor signal prompting your hand to let go. The behavior is mostly on a closed circuit, and there's no reason why all behaviors can't be on train tracks like this, with nothing but inputs and outputs as the behaviorists used to theorize. However, I said mostly because even in such reflexive loops, there is still veto power coming from another source: the brain. You can voluntarily inhibit the reflex circuit for whatever reason, like not wanting to drop and break the plate. And if you've ever been in that situation, you can feel the push and pull between your volition and the impulse to let go.

As I mentioned much earlier, autonomy is one of our most fundamental motivational needs. If you want to predict how intrinsically motivated a person will be at doing anything, measuring how much autonomy is involved is a great predictor. In other words, the brain wants to be in control and avoid external capture. Conversations like this just don't make sense without free will. You don’t build a system obsessed with agency and self-regulation if all behavior is passive output.

But of course, the problem with those who oppose free will is that they just handwave things like this as illusions.

Does the deity you believe exists, know the future, I mean does it know what we will do before we do it? Only this is where notions of autonomy, are often contradicted by beliefs in an omniscient deity, not always of course, hence the question. 

It seems obvious we have will, how free it is, is another matter. Though obviously I think it's limitations are not as a consequence of any deity.