It is a great work to believe that Christ, nailed to the cross, is the Son of God. That this is the work of God, Christ Himself testified, Jn. 6:29: “This is the work of God, that ye believe on him whom he hath sent.” As many, then, as trust in Christ are built upon a rock, which no blasts of winds can shake, no inundating floods wash away. And as many as are built upon this are the church of Christ, for He Himself said “my.” But His church cannot be impure and wrinkled. Therefore it follows that those who trust in Christ are without spot and without wrinkle, for they summon up all their zeal to the end that they may not fall back into sin, in which beforetime they were dead, Rom. 6:2. But they who do not this utter noble thunderings with their lips, but by their deeds betray Christ, with the result that through them the name of God is in bad repute.
This is the church that cannot err—an attribute which the pontiffs arrogate to themselves with as much falseness as impudence. For this church rests upon the word of God alone, which is so firm and immovable that heaven and earth must pass away sooner than one jot of it [Mt. 5:18]. On the contrary, the church of the pontiffs rests upon its own word. They run, indeed, as if they had been sent by the Lord, but they speak visions, that is, things pleasing to their own heart [Jer. 23:16]. Hence they spread nothing but darkness before poor wretches’ eyes.
Zwingli: The Smartest Guy in the Room