Rene Descartes / Meditations - Essential Summary
Rene Descartes' "Meditation of the First Philosophy" is written as a firsthand account of thoughts which occurred to Descartes in the course of six days (meditation per day) in which he withdrew from the world in order to find a firm and proven basis for his understanding of reality.
Descartes opens "Meditation" with an apologetic statement (perhaps in fear of the Inquisition), explaining that he does not promote heresy but rather a deeper devotion and a way for skeptics (abounded in Descartes' times) to come back to religion.
The first meditation of the book starts from this skeptic approach and Descartes describes how many things he held to be true turned out the be wrong. He sets his task as finding something which cannot be doubted to be true, arguing that this thing can be the secure a stable basis for constructing valid knowledge of the world. This move draws on Descartes' need for an established method to inquire into reality, discussed in his "Discourse on the Method".
Descartes establishes his skepticism by methodically exploring the origins of knowledge, doubting them all in order to find out what remains beyond all doubt. He rules out the senses which can be deceiving, but also our ability for non-empirical knowledge. To end the debate, Descartes offers the thought of a malicious demon which constantly fools us. Since the demon hypothesis cannot be univocally defeated, Descartes finds himself in the end of meditation 1 unable to know anything.
Descartes continues to wonder if he himself in fact exists. He gives his famous answer (the cogito) holding that I for sure exist. Deceived and erroneous as I may, there is still an "I" who is wrong and deceived (and in the famous formulation: "I think therefore I am").
Existing is good, but Descartes wonders what else I can know about reality. The following thing after proving the self is proving that God exists. in the later chapters of "Meditation" Descartes gives three philosophical proofs of God's existence. The important thing about God for Descartes is that his benevolent and eternal perfection are a source of validation to all I know. This knowledge for Descartes is not the dogmatic church but rather the inner individual capacity for rational thought, a type of methodical proof-seeking type of thought he calls science.
See also A summary by chapter of Descartes' Meditations:
Descartes / Meditations - Summary by Chapter
"Meditations of the First Philosophy In which the Existence of God and the Immortality of the Soul are Demonstrated" (1641) is René Descartes most notable philosophical work (alongside "Discourse on the Method" which precedes "Mediation" and sets its theoretical framework). Descartes' "Meditations" is considered to be the opening shot of western modern philosophy for it establishes its fundamental question such as epistemology and the Rationalist/Empiricist debate.
Descartes' "Meditations" is made out of six chapters, six meditations, one for each day of Descartes' firsthand account of his withdrawal from the world with the purpose of finding an absolute and secure basis for his knowledge of the world. Descartes starts with doubting anything he knows, moves on to finding a reason to be believe he himself exists and finally to proving god exists and therefore anything else.
Here you can find an essential summary of Descartes' Meditations outlining the main arguments and notions of the book. You can also find a detailed account of Descartes' arguments for the existence of God in Meditations.
For a detailed summary of Meditations by chapter/meditation see:
Chapter / Mediation 1: On the things that may be called Into doubt
Chapter / Mediation 2: On the nature of the human mind and that it is easier to understand than bodies
Chapter / Mediation 3: On the existence of God
Chapter / Mediation 4: on truth and falsity
Chapter / Mediation 5: On the essence of material things and the existence of God once more
Chapter / Mediation 6: On the existence of material things and the real distinction between the mind and the body
Each chapter summary contains the main ideas presented in the meditation and the general course of Descartes' thought. The summaries end with a brief explanation of how the meditation relates to all other meditations of Descartes' book.