Engine cranks but it does not start, could it be the Anti-theft system?

Okay, here is an easy test to see if it is the immobilizer: put the key in and turn it on. What does the security light do? If it goes out it's not the immobilizer, if it starts blinking then the key isn't being recognized and you either have a bad key or the more common issue which is the module in the column has failed. Now if you don't see a security light come on at all don't be surprised, the immobilizer wasn't standard on the Quest until after 2004 and if you are hearing the fuel pump run it also isn't the immobilizer as it shuts off the fuel pump.
I would start with the basics, you say it has fuel, have you tested for spark? I would start there, remove a plug on each side and see if you have spark. This might help as a start.
https://www.2carpros.com/articles/car-not-running-advanced
Let us know what you find, and we will have a starting point.