"It was given to her what belongs to no creature, that in the flesh she should bring forth the Son of God" [Ulrich Zwingli, In Evang. Luc., Opera Completa [Zurich, 1828-42], Volume 6, I, 639]
A simple Goggle search of this quote demonstrates excessive cut-and-pastes. From a conservative Protestant perspective, there isn't anything outrageous about this quote. It's true: Mary was uniquely chosen to give birth to Jesus Christ. Why then do Roman Catholics use this quote? Before answering this question, let's take a closer look at where the quote came from.
DocumentationThe reference "Evang. Luc., Opera Completa" is accurate, but I have doubts modern Roman Catholic apologists found this old text and mined out this quote, translating it into English. A Roman Catholic apologist at some point in the past came across a secondary source citing it and cut-and-pasted the quote into cyberspace. For instance, an exact early Roman Catholic English usage can be found in Theotokos: a Theological Encyclopedia of the Blessed Virgin Mary (from1982):
The Swiss Reformer expressed views somewhat similar to Luther’s; but there were certain differences due to his singular outlook. His ideas on Mary are found mostly in a Marienpredigt and in his commentary on Lk and the controversial writings. The sermon is praise of the divine motherhood and perpetual virginity: “it was given to her,” he says, “what belongs to no creature, that in the flesh she should bring forth the Son of God." (In Evang. Luc., Op. compl., 6.1,639)
Maria ist heilig, ja sie ist nach Zwinglis Worten das hei= ligste aller Geschöpfe, aber nicht aus sich selber und nicht an sich; ihre Heiligkeit stammt aus der Heiligkeit Christi: Diese Worte (Luk. ı, 42) sind nicht so zu verstehen, als ob Maria irgend welche Seligkeit Christo gegeben, oder sie selber in sich eine solche Seligkeit besessen hätte, sondern beziehen sich mehr auf das Lob Christi. Dies wird nicht dazu gesagt, als ob wir damit meinten, Maria sei nicht ganz selig gewesen: denn es ist ihr gegeben, was keiner Kreatur (sonst) zukommt, daß sie im Fleische den Sohn Gottes gebar, was aber nicht der Kreatur zugeschrieben werden kann, weil es einzig Gottes ist. Die Frau sagt also dies: Ihr Pharisäer schmäht das Werk Christi und ihr schreibt diese Macht den Dämonen zu. Ich aber verkündige gegen euch, er sei der heiligste von allen, daher selig, so daß auch seine Mutter und ihr Schoß selig sind. Die Heiligkeit der Maria stammt also aus der Heiligkeit Christi, nicht umgekehrt! (6; 639)
Mary is holy, indeed, according to Zwingli, she is the holiest of all creatures, but not by herself and not in itself; her holiness comes from the holiness of Christ: These words (Luk. ı, 42) are not to be understood as if Mary had given any kind of blessedness to Christ, or as if she herself had such blessedness within herself, but rather refer to the praise of Christ. This is not said as if we meant that Mary was not entirely blessed: for it was given to her which is not due to any creature, that she gave birth to the Son of God in the flesh, but which cannot be attributed to the creature, because it is only God's. So the woman says this: You Pharisees revile the work of Christ and you attribute this power to demons. But I declare against you that he is the holiest of all, and therefore blessed, so that his mother and her womb are also blessed. The holiness of Mary comes from the holiness of Christ, not the other way around! (6; 639)
Beatus venter qui te.) Haec ergo verba non sic intelligi debent, quasi Maria Christo aliquam beatitatem dederit, aut quod ipsa in se talem beatitudinem habuerit, sed potius pertinent ad laudem Christi. Haec non in hoc dicuntur, quasi diceremus Mariam non fuisse beatis- simam: datum est enim ei quod nulli creaturae contigit, ut in carne generaret filium dei; sed quod non debet tribui creaturae quod solius est dei. Mulier ergo sic dicit,: Vos pharisaei calumniamini factum Christi, et daemoni adscribitis hanc virtutem. Ego autem contra vos pronuncio ipsum esse sanctissimum omnium, adeoque beatum, ut etiam mater eius et uterus beata sint. Sanctitas ergo Mariae ex sanctitate nascitur Christi, non contra. Dona dei sic habent: hominibus dantur et donantur ad usum aliquem et laudem dei et salutem proximi dei vero sunt; usus datus est nobis non possessio.
(Blessed is the womb that has thee.) These words, then, are not to be understood as if Mary gave some holiness to Christ, or that she herself had such holiness in herself, but rather belong to the praise of Christ. These things are not said in this, as if we were to say that Mary was not the most blessed: for it was given to her that which has happened to no creature, that she should bring forth the Son of God in the flesh; but that it is not to be attributed to a creature that belongs only to God. The woman therefore says thus: You Pharisees slander the deed of Christ, and ascribe this virtue to the devil. But I declare against you that he is the most holy of all, and so blessed that his mother and womb are also blessed. The sanctity of Mary, then, is born from the sanctity of Christ, not against it. God's gifts have this way: they are given and given to men for some use, and they are truly the praise of God and the salvation of God's neighbor; use is given to us, not possession.