The meaning of the prophecy that “G-d will remove the sun from its shield” is twofold, spiritual and physical. In a physical sense, the light that reaches us from the sun must pass through a protective layer, which absorbs some of the sun’s rays so that we are able to receive it.
In the future, the light from the sun will reach us directly, without having to pass through the protective layers. (According to Rashi’s interpretation, the sun’s light will be 343 times stronger than today.) Seemingly, this will be a harmful situation that will desiccate the earth. However, our sages assure us that a supernatural state will exist: The sun will heal the tzadikim and only the evil ones will be harmed by it.
In a spiritual sense, G-d’s radiance as it is reflected to earth is likened to the light of the sun, as the verse states (Psalms 84:12), “For a sun and a shield is Hashem Elokim [the L-rd G-d].” Just as the sun shines through a shield and without the shield we wouldn’t be able to withstand its radiance, so, too, does the spiritual light reaching us from G-d pass through a shield, Elokim. The word Elokim, L-rd, in Hebrew has a numerical value of 86, same as the word Hateva, the natural world. This is the purpose that G-d’s name Elokim serves--it is a shield, filtering out the full intensity of G-d’s light, so the natural world will be able to withstand it.
In the future, G-d will remove the sun from its shield. In other words, He will remove the covering of Elokim and will shine forth directly from the name of Hashem. However, the evildoers will not be able to withstand this level of light. For them, the name of Hashem, normally representing G-d’s attribute of compassion, will become the attribute of judgment, as our sages say, “The evil ones will be judged by it.” The tzadikim, however, will benefit from it, since they will be fit to withstand this great revelation of light from above.
Nedarim 8b; Rashi on Isaiah 30:26; Keser Shem Tov, Chapter 246.