Luther and Zwingli disagreed on which doctrine and why ?
Soon he had risen to prominence in the city , and when political tension developed between most of Switzerland and the Catholic Habsburg Emperor Charles V. In this environment , Zwingli began preaching his version of reform , with certain points as the aforementioned doctrine of justification , but others ( with which Luther vehemently disagreed ) such as the position that veneration of icons was actually idolatry and thus a violation of the first commandment , and the denial of the real presence in the Eucharist .