Gemara: Rav Chiya bar Ashi said in the name of Rav: He who washes his hands first at the end [of the meal] is the appropriate one to make the beracha (lead bentching). Rav and Rav Chiya were sitting in front of Rabbi [Yehuda Hanasi] in a meal. Rabbi said to Rav: "Get up, and wash your hands." [Rav Chiya] saw that [Rav] was trembling and said to him: "... he was telling you to prepare to lead bentching."

Ein Ayah: The washing of mayim acharonim (at meal’s end) comes to alert one who wants to elevate himself in shleimut (completeness) that he should distance himself from the unavoidable animalistic imprint that involvement in physical enjoyment makes. Until he separates himself from the influence of the eating he is unfit to make the beracha, which requires one’s spirit to rise up to the appropriate lofty sanctity that behooves one who blesses Hashem. One who feels the tension of the animalistic influence and is first to take the proper steps to counter it (mayim acharonim) is the most appropriate one.
Therefore, the halacha was set to illustrate the connection between mayim acharonim and becoming elevated by the beracha to the love of Hashem. Rabbi instructed Rav to wash rather than to tell him explicitly to bentch in order to hint that only the unavoidable materialistic imprint that is found in every person, who is materialistic, prevented Rav from being fit for the beracha.
Rav trembled because he feared that Rabbi wanted him to remove an extra level of the materialistic imprint that mayim acharonim hints at. However, Rav Chiya assured him that Rabbi was referring to only the minimum level that exists in every corporal being who receives physical enjoyment, for which no one is to be blamed.
When one takes the steps to overcome the negative physical influence, he can appreciate how food is very fit to bless upon, for it need not cause one a spiritual loss but is all good and a favor for us. It is physical desire that is the direct cause of lacking in several areas. When he enjoys, washes his hands, and removes the ingrained problem, he will be able to receive the proper benefit from the food. For when man is sanctified, his materialistic inclinations become important utensils for obtaining great success, and for this they are deserving of a beracha.

The Proper Level of Asthetics
(condensed from Ein Ayah, Berachot 6:52)

Gemara: A talmid chacham should not go out with patched up shoes. Is that so? Didn’t Rabbi Chiya bar Abba go out [that way]? Mar Zutra the son of Rav Nachman said: The problem is with a patch on top of a patch.

Ein Ayah: It is proper that a complete person not be to drawn to feelings of beauty to the point that he is enslaved by them and unable to bear something that lacks charm and external beauty. If that happens, then the aesthetic sense, which was given to him to enhance his life, broaden his mind, and bring joy to his spirit, will turn into a source of depression, for when his sense of aesthetics is not reached, he will be troubled and disappointed.
On the other hand, one should not betray the tendency toward beauty to the point of erasing this important feeling. After all aesthetics can elevate the spirit and prepare man to know truth and true honor, as it can play significant role in knowing Hashem and enjoying His goodness and grandeur.
Rav Chiya bar Abba reached the following balance. He went out with patched shoes to show an element of not caring and certainly not being enslaved by the pleasant desire for beauty. Yet, he did not go out with patches on patches, which would have openly robbed aesthetics of a place as something of use and value. The two opposing messages he sent led to a path of moderation.