Traditionally, we have believed that the darkest period of the galut (exile) will occur immediately prior to the coming of the Messiah. In those final years before redemption, morality and even simple decency will be hard to find. Authentic spirituality will disappear, and the world will be rife with heresy. As the Talmud states:
R. Nehorai said: In the generation when the Messiah comes, young men will insult the old, and old men will stand before the young; daughters will rise up against their mothers, and daughters-in-law against their mothers-in-law. The people shall be dog-faced, and a son will not be abashed in his father's presence.
R. Nechemiah said: In the generation when the Messiah comes, impudence will increase, none shall esteem another...and the government of Israel will be converted to heresy. This supports R. Yitzchak, who said: The Messiah will not come until the government of Israel is converted to the belief of the heretics.
Rabbah said: What verse proves this? "It is all turned white; he is clean." (Sanhedrin 97)
This doctrine is hard to understand for two reasons. Why would Rabbah choose the symbolism of "whiteness" to represent the darkest period of the galut? And why does the Talmud claim that the spread of heresy will usher in the coming of the Messiah? Would it not make more sense, though, to assume that in the years immediately before the Messiah's arrival we will witness an increase in religious observance?
To answer the first question, let us refer to Rav Yosef Dov Soloveitchik's explanation of the symbolism of white and blue. (See Reflections of the Rav vol. II, ch. 2 for an expanded discussion of this symbolism.) White denotes clarity and lucidity, that which is rational and logical. In modern Hebrew and in talmudic Aramaic, "chavar" (literally translated as "white") means "clear" or "proven." Blue, however, represents mystery and ambiguity, the esoteric or even mystical truths which cannot be proven scientifically.
A spiritually healthy person must be able to incorporate both white and blue into his or her personality. White, the ability to think clearly and rationally, is a gift from God, and can be used as a tool for divine service. But excessive faith in the proven and the rational can lead people to reject God, who conceals Himself in mystery and refuses, for the most part, to allow us direct apprehension of His being. When a person accepts as true only that which he can measure and prove--when he becomes totally "white"--he opens himself to arrogance and ultimately to heresy.
When the Messiah's salvation is most needed God will send him to redeem the world. It is precisely in that generation that his salvation, viewed against his generation's prevalent heresy, will be most clearly highlighted and meaningful.
Aside from an important insight into the nature of the messianic process, Rav Yitzchak, more globally, teaches us that holiness is best appreciated when viewed in contrast with non-holiness. And as is the case with the ultimate redemption, distinguishing holiness from the profane may be necessary to fully appreciate holiness.
This explains a fundamental halachah regarding the donation of terumah and challah. The Mishnah (Challah 1:9 and Terumot 4:5) states that one cannot dedicate his entire batch of dough as challah, nor can he dedicate his entire harvest to be terumah. The Talmud (Chullin 136a) provides a biblical source for this rule: the Torah calls challah and terumah "reishit" or "the first portion" of the dough and harvest. As such, the donation must remain a portion of a greater whole; it may not encompass the entire thing.
But challah and terumah are not the only priestly gifts declared as "reishit." The Torah also commands us to give the Kohen the first of our yearly wool sheerings - Reishit HaGez. Yet there is no parallel law stating that we must donate only a portion of our wool to the Kohen. Why may we dedicate all of our wool as a priestly gift but not all of our dough and grain?
The Melechet Shlomo (Challah 1:9) quotes the following answer. The only time the term reishit indicates that only a portion of the whole may be donated is when the gift itself is inherently holy. Challah and terumah are two such cases. Both may only be consumed by a ritually pure Kohen, both have strict laws regarding their handling and donation and both prescribe severe punishments for those who desecrate their sanctity. In these cases, the Torah demands that we distinguish the donation and highlight its kedushah by leaving over a portion of dough or grain to remain plain and ordinary.
Wool of the Reishis HaGez contains no kedushah, as shown by the lack of strict rules regarding its handling and consumption. Since it has no kedushah to highlight, there is no need to distinguish it by contrasting it with remaining wool. The entire batch of wool may therefore be donated.
Our Rabbis' insight into the messianic era and the detailed laws of challah and terumah are two sources that not only emphasize the importance of distinguishing between the holy and non-holy, but also demonstrate that the distinction itself may grant us a fuller understanding and appreciation of true holiness.