This is taken from Perry Miller’s exposition. I will place letters (a, b…z) throughout the paragraph to better order the argument. They are not original to Miller.
If the will determines its own act [per Arminianism], there must always be a will before the act. Each act must be preceded by an act of the will, and that by another, and so on, ad infinitum, until we come to the theoretical first act; if this is determined by a still previous act of the will, we take up the march again, but if we call a halt, (a) and this act is first, we have an act that flows from no volition, which is just simply an act, (b) arbitrarily given, which cannot be the selection of a free will (p. 259).
Edwards’/Miller’s argument is interesting on several levels. He highlights that a rejection of Calvinism actually brings the denier to the very stereotype of Calvinism that he so strenuously avoided. If we accept the premise that every act flows from a will, then we are either left with an infinite series, which does us no good because we are not infinite and can never get to the beginning, or (a), which appears to be the stereotype of Calvinism. However, (a), divorced from a Calvinist system, leads to chaos, given (b). At this point, man is both chaotically free and a robot. Edwards neatly anticipated existentialism and reduced his opponents to this absurdity.