"Zwingli...was at heart a Thomist, which he remained even as a Reformer--a Thomist for whom revelation never can contradict reason. For him, as for Thomas, God was "primum movens" and "prima causa," the first cause of, and the deepest reason underlying all things. What reason is in man, that God is in the world..."God is truth and He is light. He gives light and does not lead us into darkness," as Zwingli said at Marburg. Here is perhaps the deepest contrast between him and Luther who in the Word of God always found that which contradicts human reason. That the wisdom of God is hidden under the appearance of foolishness, the truth of God under what seems to reason to be a lie, and that the Word of God always comes to us as something that contradicts our mind, Zwingli would never have been able to say."--Hermann Sasse, This is My Body, pp. 117-118
Clinging too tightly to Christ's Words is never the problem. Rationalism is the problem. Luther's beef with the Roman Church was that they made an Aristotelian philosophical assumption a matter of religious dogma. Thomas Aquinas taught that the presence of Christ's body and blood is not to be understood as a local presence but substantially. Thomas taught that Christ's body is situated in heaven in a particular place. Luther was determined to simply cling to the Words of Christ without all this philosophical speculation. So did Zwingli go beyond Luther in his reforms? Absolutely not! Zwingli ran the other direction. He took the path of rationalism that Luther was criticizing in Thomas. Zwingli agreed with Thomas that Christ must be situated at some fixed location in heaven and took the further step of denying the substantial presence of Christ in the sacrament.