ultimately, what gets lost in all of this is:
think of all this like a court room of sorts.
the bible/whatever your holy text is, is your theory of how the world came to be or how life came to be. the science textbook is our proof that your theory is wrong. when you take the time to go through our documents and proofs, when you take the time to perform the experiments to verify the proofs and you go physically see the archaeological/anthropoligical/astronomical evidence for the proofs, then you will see why your theories are wrong.
the more in depth answer to the flat/sphere:
the concept of sphere and flat are based on unchanging laws of math. these are based off of equations that are proven true when graphed on cartesian coordinates and in 3 dimensions. 3dimensions is an extension of cartesian planes which are derived from the number line and we all know how to count. the number line is one of the very first things you ever learned