Since God exists in an idea, this premise moves Descartes closer to dealing directly with the idea of God. Since an idea is a representation of some thing or things, all ideas have objective reality contained in the representation of the formal reality of their referents. By invoking this premise, Descartes can move into the realm of reality in an effort to eventually reach the formal reality of God. There must be at least as much objective reality in the cause of some effect than in the effect alone. This premise enables Descartes to move beyond the isolated event of some idea, i.e. God, and trace its origin.
Every idea has a cause.
From this premise, Descartes can begin to trace the idea of God in search of a measure of its formal reality and thus its existence. For every idea, if one were to discern the cause of the idea and the cause of that idea and so on, one would eventually discern some first idea whose cause contains formally all the reality that is in the idea merely objectively. The idea of God is a certain substance that is infinite in independence, intelligence and power. This premise simply presents the idea of God so that Descartes can utilize the previous logic to get at its formal reality. I do not contain, formally, infinite independence, intelligence and power.