The idea of omnipresence as a quality of a chief god is known in antiquity. The Stoics, for example, conceived of God as material, permeating all matter and endowing it with the qualities of heat, movement, order and reason.
Indeed, all pantheism and panentheism entail the idea of a being who's everywhere at once. Thus they occur in eg old Vedic belief systems.
Once you have regard to Einstein, the idea of being everywhere in space becomes the idea of being everywhere in spacetime. Thus God perfectly knows everything that has happened, is happening, and will happen, down to the tiniest detail, the most trivial relationship, and for several reasons. First, because God is omniscient, second because God is perfect and therefore could make perfect guesses at anything not manifest, and third, because being omnipresent in spacetime God's looking at it right now.
Thus freewill is impossible, and humans can only ever think, say and do exactly what God foresaw (and thus intended) even before God made the universe. We have the illusion of free choice but we can only do exactly what we were always going to do.
Or else, of course, God is not omni at all, doesn't even exist at all, and humans lack freewill simply because the universe is physical and proceeds in terms of cause-and-effect and quantum randomness.