Our Gemara on Amud Aleph discusses the susceptibility of a Red Heifer to become impure (something that only applies to a food item that at least at one time was ready for consumption and can be consumed.) This is because the Red Heifer could be potentially redeemed, and then eaten. Therefore, even if it is highly unlikely to actually be redeemed, it still has the legal status of an edible food item because of the potential to do so.
Gemara Moed Kattan (28a) notes:
אָמַר רַבִּי אַמֵּי: לָמָּה נִסְמְכָה מִיתַת מִרְיָם לְפָרָשַׁת פָּרָה אֲדוּמָּה? לוֹמַר לָךְ: מָה פָּרָה אֲדוּמָּה מְכַפֶּרֶת — אַף מִיתָתָן שֶׁל צַדִּיקִים מְכַפֶּרֶת.
Rabbi Ami said: Why was the Torah portion that describes the death of Miriam juxtaposed to the portion dealing with the red heifer? To tell you: Just as the red heifer atones for sin, so too, the death of the righteous atones for sin.
The Ateres Yeshua (Chukas) sees symbolic meaning in the halachos described in our Gemara that relate to the idea of a tzaddik in this world. (I am adapting his thoughts and expressing them differently to make certain points. For his original ideas on this, please check out the primary source.) The Tzaddik exists in this world similar to the Red Heifer. We know the Red Heifer had an unusual quality of purifying the impure, but rendering the pure impure (Yoma 14a). Ateres Yeshua says this is similar to the mission of the Tzaddik, who must enter into the physical world and elevate it. He first enters the realm of the impure, becomes involved In physicality, but then elevates it. This is metaphorically represented in the halacha that the Red Heifer is considered food because of its potential to be redeemed. The physical in this world (food) can be considered true spiritual sustenance because it has the potential to be elevated.
Lest you think this is some arcane chassidic philosophy, we find the exact sentiment expressed in the final chapter of Mesilas Yesharim.
וְהִנֵּה הָאִישׁ הַמִּתְקַדֵּשׁ בִּקְדֻשַּׁת בּוֹרְאוֹ אֲפִלּוּ מַעֲשָׂיו הַגַּשְׁמִיִּים חוֹזְרִים לִהְיוֹת עִנְיָנֵי קְדֻשָּׁה מַמָּשׁ, וְסִימָנָךְ אֲכִילַת קָדָשִׁים שֶׁהִיא עַצְמָהּ מִצְוַת עֲשֵׂה, וְאָמְרוּ זַ"ל (פסחים נט ב): כֹּהֲנִים אוֹכְלִים וּבְעָלִים מִתְכַּפְּרִים.
Behold, for the man sanctified with the holiness of his Creator, even his physical deeds become actual matters of holiness. A sign of this is in "the eating of temple offerings", which our sages of blessed memory said: "the priests eat and the owners obtain atonement" (Pesachim 59b).
וְאָמְנָם לְפִי שֶׁאִי אֶפְשָׁר לָאָדָם שֶׁיָּשִׂים הוּא אֶת עַצְמוֹ בַּמַּצָּב הַזֶּה כִּי כָבֵד הוּא מִמֶּנּוּ, כִּי סוֹף סוֹף חָמְרוֹ הוּא בָּשָׂר וָדָם, עַל כֵּן אָמַרְתִּי שֶׁסּוֹף הַקְּדֻשָּׁה מַתָּנָה, כִּי מָה שֶׁיּוּכַל הָאָדָם לַעֲשׂוֹת הוּא הַהִשְׁתַּדְּלוּת בִּרְדִיפַת הַיְּדִיעָה הָאֲמִתִּית וְהַתְמָדַת הַהַשְׂכָּלָה בִּקְדֻשַּׁת הַמַּעֲשֶׂה
However, it is impossible for a man to place himself in such a state. For it is beyond his ability. He is after all a physical creature, of flesh and blood. Thus I said that the end of Holiness is a gift. For that which is in man's ability to do is the initial exertion, pursuing true knowledge and continual thought on the sanctification of deed.
וְהִנֵּה אִישׁ כָּזֶה הוּא עַצְמוֹ נֶחְשָׁב כַּמִּשְׁכָּן, כַּמִּקְדָּשׁ, וְכַמִּזְבֵּחַ, וּכְמַאֲמָרָם זִכְרוֹנָם לִבְרָכָה (בראשית רבה מז:ח): וַיַּעַל מֵעָלָיו אֱלֹהִים (בראשית לה:יג), הָאָבוֹת הֵן הֵן הַמֶּרְכָּבָה, וְכֵן אָמְרוּ (רש"י בראשית לה:יג): הַצַּדִּיקִים הֵן הֵן הַמֶּרְכָּבָה.
Such a man is himself considered as a tabernacle, a temple and an altar. This is as our sages said (Gen. Rabba 62:6): "'and G-d went up from him' (Gen.35:13) - the forefathers are the divine chariot". Likewise, they said: "the righteous are the divine chariot".
כִּי הַשְּׁכִינָה שׁוֹרָה עֲלֵיהֶם כְּמוֹ שֶׁהָיְתָה שׁוֹרָה בַּמִּקְדָּשׁ. וּמֵעַתָּה הַמַּאֲכָל שֶׁהֵם אוֹכְלִים הוּא כְּקָרְבָּן שֶׁעוֹלֶה עַל גַּבֵּי הָאִשִּׁים, כִּי וַדַּאי הוּא שֶׁיִּהְיֶה נֶחְשָׁב לְעִלּוּי גָּדוֹל אֶל אוֹתָם הַדְּבָרִים שֶׁהָיוּ עוֹלִים עַל גַּבֵּי הַמִּזְבֵּחַ כֵּיוָן שֶׁהָיוּ נִקְרָבִים לִפְנֵי הַשְּׁכִינָה.
For the Shechina (divine presence) dwells within them just as it dwelled in the Temple. Due to this, the food they eat is like a sacrifice offered upon the fire of the altar, for certainly it was a great elevation for those things to be offered on the altar, since they were offered before the Shechina.
וְכָל כָּךְ יִתְרוֹן הָיָה לָהֶם בָּזֶה, עַד שֶׁהָיָה כָּל מִינָם מִתְבָּרֵךְ בְּכָל הָעוֹלָם, וּכְמַאֲמָרָם זַ"ל בַּמִּדְרָשׁ, כֵּן הַמַּאֲכָל וְהַמִּשְׁתֶּה שֶׁהָאִישׁ הַקָּדוֹשׁ אוֹכֵל, עִלּוּי הוּא לַמַּאֲכָל הַהוּא וְלַמִּשְׁתֶּה הַהוּא, וּכְאִלּוּ נִקְרָב עַל גַּבֵּי הַמִּזְבֵּחַ מַמָּשׁ. וְהוּא הָעִנְיָן שֶׁאָמְרוּ עָלָיו זַ"ל (כתובות ק"ה ב): כָּל הַמֵּבִיא דּוֹרוֹן לְתַלְמִיד חָכָם כְּאִלּוּ הִקְרִיב בִּכּוּרִים. וְכֵן אָמְרוּ (יומא עא א): יְמַלֵּא גְּרוֹנָם שֶׁל תַּלְמִידֵי חֲכָמִים יַיִן בִּמְקוֹם נְסָכִים.
The elevation was to such an extent that its kind, all over the world, was blessed, as our sages stated in a Midrash. So too, the food and drink which the holy man eats elevates that food or drink as if it had actually been offered on the altar. This is similar to what our sages, of blessed memory, said: "one who brings a gift to a Torah scholar is as if he had offered first-fruits (Bikurim)" (Ketuvot 105b), and "[if a man wishes to offer a wine libation upon the altar], let him fill the throat of the Torah scholars with wine" (Yomah 71a).
At the time that Ramchal wrote Mesilas Yesharim, he was under a Herem to no longer write Kabbalistic works (see https://en.wikipedia.org/wiki/Moshe_Chaim_Luzzatto ).
Out of what must have been incredible internal pressures, and even dare I say, frustration, arose one if the greatest human written achievements of all time. Like a diamond, Mesilas Yesharim was formed under intense forces and pressure. Without saying one word of Kabbalah, he wrote a classic of ethics that must have hidden kabbalistic undertones. This comes clear in the final chapter where he described the role of the Tzaddik in elevating the material world (only after first having totally mastered ascetics.)
As a final point, this discussion takes place on what is one of the shortest dappim in Shas, and the Ramchal himself lived for less than 40 years. The Tzaddik, a living Parah Adumah, embraces the opposites. He takes the physical and makes it spiritual. He may have a short life, but is most alive. He can be forbidden from expressing kabbalah openly, but writes one of the greatest religious tracts of all time. Paradox inside paradox.
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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