Complex sentence: Descartes claimed that the only cause to the idea of God must be God himself, but according to hume God is a complex idea formed with simple idea caused by simlpe impressions, therefore the idea of God doesn't require God neither proves his existence.
Split into simpler sentences: Descartes claimed that the only cause to the idea of God must be God himself, but according to Hume, God is a complex idea formed from simple ideas caused by simple impressions. Therefore, the idea of God doesn't require God neither proves his existence.