The following is excerpted from Getting the Reformation Wrong: Correcting Some Misunderstandings by James R. Payton Jr. (IVP, 2010). The quotes by Zwingli are from his Commentary on True and False Religion, written in 1525.
Ulrich Zwingli also stressed the mercy of God for the justification of unworthy sinners. He wrote, “This is the gospel, that sins are remitted in the name of Christ; and no heart ever received tidings more glad.” Zwingli proceeded to expand on this teaching, eventually stating:
“For when man through repentance has come to the knowledge of himself, he finds nothing but utter despair. Hence, wholly distrusting himself, he is forced to take refuge in the mercy of God. But when he has begun to do that, justice makes him afraid. Then Christ appears, who has satisfied the divine justice for our trespasses. When once there is faith in Him, then salvation is found; for He is the infallible pledge of God’s mercy.“
He wrapped up his treatment by asserting: “Through Christ alone we are given salvation, blessedness, grace, pardon, and all that makes us in any way worthy in the sight of a righteous God.“ (pg. 120)