Thus you shall keep the people of Israel separate from their uncleanness, lest they die in their uncleanness by defiling my tabernacle that is in their midst. (Vayikra / Leviticus 15:31; ESV)
This is perhaps one of the most important statements in the Torah in helping us to understand the implications of the New Covenant. Vayikra (the Book of Leviticus) contains detailed instructions regarding how the community of Israel was to deal with spiritual uncleanness.
The term unclean in Hebrew is "tamei". It does not mean unclean in the sense of being dirty, but rather it is the defilement of spiritual purity. When someone or something is "tamei," they are unfit to be in God's presence or to be used in God's service. Not only did the defiled person risk death by being in God's presence, their defilement also defiled God's dwelling.
I will explain. God's plan and purpose for creating the people of Israel was to make himself known to the world. God instructed the people of Israel through Moses to construct a tent-like structure called the Mishkan (English: Tabernacle), which would later become a permanent structure called the Temple. The Mishkan and the Temple represented God's dwelling place. The various inner sections of these structures, while providing, in some sense, access to God, actually illustrated the barriers that existed between us and him.
Much of the sacrificial system was to deal with the issue of defilement. On one hand it allowed people to engage God by undergoing ritual cleansing, but at the same time it continually reminded them how they, as an example of the condition of all people, were unfit to intimately engage God.
Many of the things that defiled a person, which in turn threatened the purity of God's dwelling, were unintentional, including certain diseases, bodily emissions, and child birth. While immorality was also defiling, it was necessary to learn that human defilement was involuntary. Being unfit to approach God was part of our natural human state.
The Torah's teaching on defilement, therefore, describes our predicament before God. Even though the people of Israel were called to be God's people, human nature derived as it is from our first parents is unable to engage our Creator as he originally intended.
It is this predicament that the Messiah came to resolve. He, who in his nature, was completely undefiled, took on our defilement, so that we can approach God freely and fully. The New Covenant book of Hebrews details how Yeshua purified God's heavenly dwelling of which the earthly Mishkan was a model. Our defilement defiled God's dwelling place and kept us alienated from him. But the sacrificial blood of the Messiah, the Son of God, removed the effects of our defilement, making all who trust in him eternally pure, and thus absolutely fit to be in God's presence.
It is no wonder then that not long after Yeshua's coming the Temple was destroyed. There is no longer any need to go through the motions of purification or to be reminded of our defilement, since Yeshua has made us pure once and for all.