In the days when the Temple stood, there was a daily battle with this 'evil' entity, for whenever a Mincha — a meal-offering consisting of flour was brought, the priests would have to be most diligent in the processing of this sacrifice to assure it would not become leaven and remain Matzah. 

No meal offering that you sacrifice to the Lord shall be made [out of anything] leavened. For you shall not cause to [go up in] smoke any שאור — leavening or any דבש — fruit-honey, [as] a fire offering to the Lord; (Vayikra 2 11)

The Talmud in analyzing this verse determines that 'No meal offering shall be made leavened' refers to the entire meal-offering, even 'שירים'  — the leftover meal that remains behind after separating a קומץ, a threefingersful of the meal-offering that is to go up in smoke upon the altar — are to be eaten by the Kohanim and remain unleavened.

It further states that the additional prohibition of not burning upon the altar any fruit-honey, only applies to not adding it to the threefingersful that are consumed by the fire on the altar. However, the remnants of the meal-offering eaten by the Kohanim may be enhanced with fruit-honey.

Lastly, although these two ingredients are taboo to any meal-offering, there are two exceptions.

[However,] you shall bring them as a first [fruit] offering to the Lord; nevertheless, they shall not go up on the altar as a pleasing fragrance. (ibid 12)

The 'first offering' here refers to the שתי הלחם — Two Leavened Loaves that are offered on Shavuos, and בכורים — the first produce of the seven species for which the Land of Israel is praised, that are presented to the Kohen and placed near the altar.

The Two Loaves are leavened, and the First Fruits are sweet, especially dates and figs, as honey in the verse refers to the sweet honey-like nectar of these fruits.

What is so pernicious about leaven? Why is it precluded not only from the Kometz that is burned on the altar but prohibited on the 'leftovers' too?

Why is something sweet shunned, and why is it only from the Kometz that is burned on the altar and not from the remnants that are eaten?

If they are so dangerous then why do we bring not only leaven but sweet fruit too on the day of the giving of the Torah, Shavuos?

There are two instinctive drives within every human being — to be independent, and to possess our wants.

The baking of leavened bread requires that most valuable of all assets — time. One who is bound to the dictate of others must hasten the baking process to produce his daily bread as unleavened, since he does not possess the leisure of time to allow it to rise.

The presence in our world of fruits that provides nutrition, immediate consumption, and sweet enjoyment is symbolic of man's instinct to possess all his needs and pleasures.

Rav Hirsch explains that although these seem to be objectives; the pursuit of independence and the delight in possessing my wants, are not to be construed as means, but merely results.

It is not the outcome, as many delude themselves, of our intellectual prowess and natural talent, but solely to the dictate of G-d and His benevolence.

It is only when we fathom that reality, becoming totally independent when we relinquish ourselves completely to His will, to His Torah, that we may merit the resulting successes.

נפש, a soul — a person, כי תקריב — when he brings that soul close to G-d, by presenting a קרבן מנחה — an allegiance gift, since the root of מנחה — נחה , means a leader, and thus מנחה, giving oneself over fully to His leadership, relinquishing any notion of self and submitting his will and all his accomplishments to G-d's direction, is the essence of this offering.

So, leaven — an expression of my independence, nor sweet fruit — the symbol of my successful possession of my wants, may be 'offered' by man, since it is not ours and merely a gift we have received because of our allegiance to the Torah.

On the day of Shavuos, the day the Torah was given at Mount Sinai, we are permitted to safely align our consciousness in declaring by consuming this bread of independence and indulging in our sweet gifts that the independence and possessions we merited are attributed solely through our adherence to Torah. Without that it doesn't exist.

Leaven, the symbol of false independence, can never be present at any stage and thus precluded from the Kometz and its 'leftovers'.

The sweetness of G-d's grace may be imbibed if we first pledge our awareness that what we possess is not ours, by refraining from having the audacity to 'offer' what is not ours to G-d upon the altar.

May we offer ourselves before G-d every day, even in the absence of the Temple, meriting His bountiful gifts.

באהבה,

צבי יהודה טייכמאן