Let me explain. The big bang theory suggests that the universe began in a very dense, very hot state. It also states that this very dense hot state was contained in an infinitly dense point. But to be infinitly dense it would have to be non-existant. So already we understand that the point had to be put there if this theory were truth. And this leads to the question of how did this point get there? And because we know from the laws of physics that matter can not be created nor destroyed, something outside the physical laws of the universe had to start it. Natural laws and forces could not have caused the big bang since the big bang states that all matter, time, space, and physical laws started at the initial explosion. Also the big bang is said to have been an explosion. Explosions do not bring order and if an explosion was to bring order, then there must have been a reason behind the explosion. And a bunch of nothing and chance can't make a choice. Chance can't be a cause.
Now for the steady state theory, this theory suggests that the universe is infinite. That it is steadily expanding in all directions and always will. The problem with this theory is if the universe is in a state of expansion, it would need to create more matter to sustain itself. And by physics (matter can not be created nor destroyed) we know this is impossible. And also the law of entropy tells us that the universe is winding down, in order for something to wind down it had to be wound up. Now for the theory to be true matter would always have to be created, the only logical route for one to take on the creating of matter would be something supernatural. Something that is NOT hindered by the natural laws of the universe. Something outside of time, space, and matter.