The Ba'al Shem Tov taught that Amalek (עמלק, 240), Israel's archenemy, is equal to "doubt" (ספק). No doubt that he is the original skeptic.
Amalek = doubt = "bitter" (מר). As we saw previously, a sick soul "puts bitter for sweet and sweet for bitter." For Amalek, there's nothing sweeter than to doubt.
Some people live on faith (as it says, "the tzadik [righteous one] lives by his faith"), some live on love (as the bride and groom of the Song of Songs), but others (and we mean 'other's) live on doubts. Those that live on doubts not only doubt the faith of the tzadik (that in which the tzadik believes) but doubt the very concept tzadik. They don't believe there's such a thing as a tzadik.
The Zohar states that a true tzadik is one who is able to convert "darkness to light and bitter to sweet" (the latter conversion being infinitely more difficult than the former). The tzadik calculates, so to speak, the value of the phrase "bitter for sweet and sweet for bitter" ("מר למתוק ומתוק למר") and finds it equal to 3 times "sweet", מתוק (meaning that the words "bitter for [sweet] and [sweet] for bitter", מר ל[מתוק] ו[מתוק] למר = sweet, מתוק)! It's all sweet. Bitter-sweet is the sweetest.
"Sweet" = 546 = 21 times 26, the product of God's two essential Names, Havayah (הוי'ה, 26), meaning "was, is, will be" and Ekyeh (אהיה, 21), meaning "I shall be." Sweet is the product of eternal, unchanging being and ever new manifestation.
The tzadik, in his consummate righteousness, reflects God's eternal, unchanging being. The skeptic, like Elisha Acher, who is destined (in our generation) to turn over once again and return to God and His Torah, reflects God's essential quality of never appearing the same, always manifesting anew. So new that you can't recognize Him.