If you think that an omnipotent deity is on your side, you'll radically overestimate your chances of success and end up on that battlefield doing something stup

If you think that an omnipotent deity is on your side, you'll radically overestimate your chances of success and end up on that battlefield doing something stupid like charging a machine-gun nest with a pointed stick and a holy book. Modern militaries find that training is far more effective, and the militaries known for being effective in the ancient world (for example, the Romans) found similarly. Religion follows society; religion is a formalised set of a given society's morals (i.e. chosen "acceptable" and "correct" behaviour). As society changes, so religion follows. In this day and age with religion being written down and available to everyone this now causes a great deal of trouble as people let the tail wag the dog, so to speak, and object to changes in society based on religion.