Gemara:


Ein Ayah: We have already explained (7:45; see presentation in Hemdat Yamim, Lech Lecha 5762) that the use of a cup of wine for a beracha hints at the idea of a life of abundant bounty that can be used by a complete person to accomplish good things. This is appropriate for great people and certainly for Hashem’s nation and the entirety of humanity, so that the resources can be used in relation to love and fear of Hashem and doing acts of goodness and kindness.
Man’s ability to speak is such that, in many ways, it is proper to use it only for intellectual/spiritual matters. After all, it represents that which man possesses above all other creations. One should view the fact that man uses it for his pleasures and other physical needs as a shortcoming. It is something out of the normal order for a person to be forced to use a precious instrument for things that are beneath its dignity. Therefore, it is worthwhile for there to be some sort of reminder that this situation is temporary and will exist only at the time that the world is still incomplete.
In the future, at the time we pray for, when the blessing of Hashem will "fill the cup of life," order will be restored, and powers will not be used in an unnatural manner. At that time, the power of speech will be used only for intellectual/spiritual matters. Regarding the complete, even positive, physical realm, which we represent with the cup of wine for berachot, extraneous speech will not be needed. This idea of reserving speech for the spiritual is found in the Yerushalmi (Berachot 1:2). There, Rabbi Shimon bar Yochai says that if he would have been at Har Sinai, he would have requested two mouths [so that one mouth would be reserved for Torah alone]. He was aware of the element of disgrace in using speech for physical things. This is part of a general concept that things that are used for sacred purposes should not be used for mundane matters unless there is no choice. When this compromise has to be made, it is sign of a shortcoming, one that we hope will disappear.
The idea that in the ideal, future time there should be no need for speech regarding mundane matters is especially true in regard to the Chosen Nation. After all, about those times, Israel is promised: "Strangers will come and raise your flock, the sons of foreign nations will be the cultivators of your fields, and you will be called the priests of Hashem ..." (Yeshaya 61:5). The nations will realize that full international cooperation mandates that every nation should do that which it excels at. The lot of Israel will then be in the realm of ethics and philosophy and studying and teaching the ways of Hashem. It is as the pasuk says: "This nation I created for Me, My praises they shall tell" (Yeshaya 43:21). Thus, the nations will happily relieve the nation which was meant to contemplate the divine of mundane work and toil. Thus, we will be able to reserve our faculty of speech for spiritual matters, whereas matters of physical sustenance will come to us easily.
To give expression to our recognition of this lofty dream, which will be realized, the Rabbis told us not to speak while involved in the cup of wine used for berachot.