Zwingli:

1] Therefore the birth had to be absolutely pure of every stain, because He that was born was also God. Second, on account of the nature of the sacrificial victim. For that had to be free from all blemish, as the law of Moses required, though that only applied to the purity of the flesh, Heb 9:9. How much more had the victim to be absolutely spotless which made atonement for the sins not only of all who had been, but of all who were yet to come… Of this figure I shall say nothing more, since it is perfectly clear in itself and through the notices of all who have spoken of it. Furthermore, the John who baptized the Son of God, as soon as he saw Christ coming towards him, pointed out to his disciples with the words: “Behold the lamb of God that taketh away the sin of the world!” John 1:29. Zwingli, Commentary on True and False Religion, (Labyrinth Press), pp., 112 and 113.

2] A little while after he says [Jn 1:29-31]: “John seeth Jesus coming unto him, and saith, Behold the Lamb of God that taketh away the sin of the world… The divine Baptist shows by these words that Christ is the lamb that atones for the universal disease of sin, and that he himself is preaching a baptism of repentance before Him that He may be made manifest to Israel. For when man through repentance has come to the knowledge of 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. For “he that gave up a Son for us, how will he not with him also give us all things?” Roms 8:32. Zwingli, Commentary on True and False Religion, (Durham, N.C: Labyrinth Press, 1981), 122-123.

3] Now as to those imposters who, not to keep silence when they cannot endure that all sins should be washed away through the grace of Christ (for they would rather, though they cannot make atonement, yet for pay received seen to do so)–who, I say, not to keep silence assert that Christ made atonement for original sin only, or for the sins of merely those who were before Him. Their error might be at once over-thrown by that single proclamation of the Baptist [John 1:29]: “Behold the Lamb of God, that taketh away the sin of the world”; for original sin is not the only sin in the world, and Christ takes away all the sins in the world. Yet I would by no means pass over the very clear testimony of 1 John 2:1-2, that they may not be able to plead any excuse. “Little children,” he says, “these things write I to you, that ye may not sin. And if any man sin, we have an advocate with the Father, Jesus Christ, the righteous: and he is the propitiation for our sins; and not for our only, but also for the sins of the whole world.”

With this testimony, then, I shall here be content, since it has been abundantly proved above that Christ is the means of salvation to all. Zwingli, Commentary on True and False Religion, (Durham, N.C: Labyrinth Press, 1981), pp., 155-156.

4] And again John the baptizer in Jn. 1:29, “Behold the lamb of God who takes away the sins of the entire world. Zwingli, Exposition and Basis of the Conclusions or Articles Published by Huldrych Zwingli, 29 January 1523, Pickwick Publications, vol 1, p, 16.