The best place to begin in discovering how Descartes wished the Meditations to be received is the Preface. Here he discusses his previous work, the Discourse on Method, and confesses that while he did touch upon the subject of God in this work he felt it deserved its own full treatment, which he intends to deliver now. In an earlier bit of the text, the letter of dedication, he states that "...although it suffices for us believers by faith that the human soul does not die with the body, and the God exists, certainly no unbelievers seem capable of being persuaded of any religion or even of almost any moral virtue, until these two things are first proven to them by natural reason." So Descartes's intended audience, then, will be atheists, as true believers have no use for logical proofs of God's existence. The second part of this statement raises an eyebrow for me; specifically, that the atheist will remain skeptical of any moral system unless the existence of God is demonstrated to him. I am not familiar enough with Descartes to expound upon his moral philosophy, but this brief statement seems to suggest that, for him, morality must come from God. However, this is a broad subject that requires more research, and should thus be saved for another post.
Continuing with Descartes's purpose, I know that he's out to convince atheists of the existence of God through the method of reasoned argument. Such proofs have long been sought out by philosophers and theologians, and Descartes even goes so far as to admit that all he has done is compiled what he believes to be the best of them in the clearest manner he can. With his audience in mind Descartes quickly dispatches two types of objections which are usually raised concerning the existence of God. First he shoots down claims which attribute human emotions to God. I am having difficulty thinking of the arguments to which he must be referring. Objections such as "If God is so good, then why is there evil in the world..." come to mind, but 'good' and 'evil' don't seem to be quite the "human emotions" Descartes is talking about. The second argument he mentions seems like something of a cop out on the apologist's part to me. Descartes wants to point out that our minds are finite and cannot grasp the nature of an infinite God. While I am neither a mathematician nor an expert on theories of infinite, this seems like a misuse of the concept. I wish to call into question whether or not things that are actually infinite can exist, as infinite does not denote any existing quantity. Of course, Descartes can easily side step this reply by saying that God is sufficiently more complicated than us to the point that we cannot understand his nature. With this in mind, I will agree that any objections do Descartes's argument for God's existence will need to attack the argument itself.
In regards to what Descartes wanted to find out in the work he put in to write the Meditations, I do not know that he sought to discover any knew information about the nature of reality or of knowledge (Metaphysics and Epistemology respectively). By his own admission he is using arguments which were already in existence and his ultimate goals seems to regain (after the doubting in the first meditation) the notions of God and reality which he had initially held. If I were to identify some secular contributions of the Meditations I would point out his work on what can only be described as early Philosophy of the Mind; the points at which he tries to pin down the nature of the thoughts, perception, and other features of the mind. These achievements, however, are simply backup for his main argument, and so I am not inclined to believe he set out to write the Meditations with the aim of producing any sort of breakthroughs in Metaphysics or Epistemology.
