Much has been written about Zwingli and the Lord's Supper. The two books of W.Peter Stephens should be consulted for this.
The following is a excerpt from Locher:
"Zwingli's protest against Luther's sacramental realism did not arise from rationalism, but from his Christology, out of concern for the complete and exclusive validity of the atonement which was made on the cross. If reconciliation took place there, then the comfort of the troubled soul cannot be made to depend on the celebration of the sacrament - an alternative which Luther never understood, nor could ever recognise on the basis of his presuppositions. But for Zwingli, as he never tired of saying, if the ceremony was more than a testimony to the forgiveness which God has sealed in my heart, through His Holy Spirit, for the sake of Christ - if it constitutes the very act of forgiveness, then it is nothing but a 'yearning for the fleshpots of Egypt', the first decline into medieval ceremonialism, in which faith clings to what is visible instead of to Christ, who is both in one, the manifestation and the pledge of grace (gratia praestita Dei, pignus gratiae). At this point - Zwingli cannot see it any other way - the whole of the Reformation is at stake."
(Gottfried W. Locher, 'Zwingli's Thought: New Perspectives' (Brill, 1981, p21)