Descartes' discussion begins in saying that "errors depend on the simultaneous concurrence of two causes: the faculty of knowing that is in me and the faculty of choosing" (Descartes p.38). I will first tackle the faculty of knowing, or intellect. Descartes says that it merely perceives and understands ideas, which can later have judgment passed on them (see Descartes p.38). The intellect is limited and finite because it can occur in different degrees. While some people have a simple understanding of a language others have a mastery of its grammar and syntax. But no one can have a mastery of all the mysteries of the universe.
Then there is the faculty of choosing, as Descartes calls it, or rather the will. Descartes says that he "experience[s] that it is limited by no boundaries whatever" (Descartes p.38). It is seen as infinite because unlike the intellect is does to adhere to different grades. It exists merely as a matter of being able to do or not to do something; to affirm or deny something proposed by one's intellect (see
Cited: Descartes, Rene. (1993). Meditations on First Philosophy . translated by Donald A. Cress. Indianapolis, IN: Hackett Publishing Corp.