"V'Zot Torah ha'asham kodesh kodashim hu." - This is the law of the guilt offering. It is holy of holies. - Leviticus 7:1

The asham is holy of holies. This indicates that it has a high degree of sanctity like the olah (burnt offering) and the chatath (sin offering). It is not of lesser sanctity like the shelamim (peace offerings), as we shall discuss shortly.

G-d designated a special status of the chatath and asham and called them holy of holies even though they were not completely burned on the altar as the olah was. THis is because these sacrifices were brought for sin. G-d did not want the penitent to thing that he was excommunictated and far from the level of the righteous because of his sins. Instead, he was drawn close to G-d anew and was as dear to G-d as if he had never sinned, since he repented and made up his mind never to repeat his previous sins.

Since penitents know the taste of sin, they are actually on a higher level than the righteous. Our sages thus teach "In the place that a penitent stands even the perfectly righteous cannot stand." The Talmud is speaking of the next world, the World to Come. The penitent (Ba'al Teshuva) has the advantage that he knows the taste of sin and still keeps away from it. The righteous on the other hand, has never experienced sin.

In order to demonstrate the extra love that G-d shows the penitents, G-d referes to their sacrifices as being holy of holies just like the olah which is completely burned to G-d.

However, the shelamim (peace offerings) which are brought by the righteous who do not have any sins merely as a free will offering, are called offerings of "minor sanctity" (kadashim kalim).

For the very same reason, the minchah offering is called "holy of holies." G-d wants to show the poor that their sacrifice is important to G-d even though it has a small monetary value.

Taken from Meam Loez Leviticus 1 (Book 11) pg. 138 based on Rashi on Leviticus 5:1