Argument for the existence of God from the existence of immaterial souls

[Guest Matteo97]

There is a famous argument, endorsed by many catholic philosophers (St. Alphonse Liguori to name one) which aims to prove the existence of God from the existence of (human) immaterial souls. I understand how to rule out the possibility of the creation of immaterial souls from matter (by principle of proportionate causality) however, I don't understand how to rule out the possibility of an infinite regress of immaterial souls causing the existence of another or the possibility of a non-divine immaterial soul existing from eternity.

[CatherineM]

You might get more answers by posting in Open Mic. I'm the world's worse philosopher. 

[Theoketos]

Everything which changes has a cause. There must be something to begin these changes, otherwise, there would be NO BEGINNING TO THE CHANGES. If there was no beginning (infinite regress) there would be nothing, no things, no change now.  Clearly there was as start changes so there was a beginning. This Original Changer must be unchanged or uncaused. (Following this logic, the unmoved mover must be the efficient causer, pure act, perfectly good etc...)