God, in all of his/her perfection, is very important in Descartes' philosophy. Reality and deception are big parts of Descartes philosophy, and to verify what reality is, God needs to be considered. God needs to be taken out of a religious context and be proven to exist in a way that we cannot be deceived into only thinking he's real. Religion had to be discarded completely during this proof so that Descartes can undoubtedly state that God does exist and that religious teaching had no influence in the proof. Descartes uses this proof to establish the legitimacy and validity of his future principles. Once Descartes establishes the existence of God, he leads on to 'rank' us within the hierarchy of living and non-living creatures. Descartes 'ranked' us between God, being the greatest, and nothing, being the least.
When Descartes philosophy deals with reality and what is deception, God enters the picture.
God, being an all powerful being is considered when the idea of something perfect is thought of. Since every idea must have some relevance to reality, the thought of perfection must have come from somewhere (Ex nihilo nihil fit; nothing comes from nothing). The idea of perfection must have been placed in our minds by a perfect being. Therefore God exists. The proof of God's existence is explained in different terms because the translation cannot always be correct. The main components of the proof are always present.
In Descartes meditation III, Descartes uses the idea of perfection to prove that God exists. This is one interpretation of Descartes proof of the existence of God.
1) I think, therefore I am.
2) I cannot be mistaken about the ideas that I have.
3) There can never be more objective reality in the effect (i.e., the idea) than...