Short version.
Astronomers looked up and saw that things in the sky go round in circles. The sun rises and sets, as does the moon. The planets and stars wheel around over the course of the night or the year.
Obviously, they all go around us. Because we can see them going around, and because God created Earth as an actual place with Very Important Humans in it, and everything else is a not-really-important blob. So we must be at the centre.
Also obviously, everything goes round in circles. Because circles are the perfect shape, and God is perfect; so if God makes things go round, they go roundninnperfect circles.
All going splendidly so far?
The one tiny little problem is that if you calculate the positions and movements of the stars and planets, using perfect circles that go around Earth, it doesn't match where the planets actually are.
Clearly there is a problem.
You recheck the observations with your telescope to make sure the planets really are where you thought, and you redo the maths. Still doesn't work, so you have to look again at your starting assumptions.
Obviously God is right. No need to check that.
Obviously Earth in the middle is right.
It has to be circles....
Ah, but it could be more circles. Instead of planets going round Earth, they are going round little invisible axes as well as going round Earth.
That nearly makes the maths work, so must be the right answer.
Except it still doesn't quite fit.
Must need more circles.