Rene Descartes 'Meditations'

In meditations by Rene Descartes, he said he has decided to doubt everything he previously believed to be true and instead rely on only his reasoning ability starting from the scratch and building his knowledge beginning with things of which he is completely certain. He rejects the knowledge from his sense deciding that such knowledge is unreliable and open to deception so is not trustworthy. He reasons that he himself must actually exist because he is able to doubt and to think. He knows that he himself exists and that he is able to think and also trusts his ability to think. He has a clear and instinct idea about his own existence. And he is certain over this.
Also, He goes on to convince himself of God’s existence reasoning that he could