The principal trend of ritual as described in the Torah is to create a setting worthy of the Divine Presence, a sanctified and pure place where the Lord will grace us by dwelling there. It is highly desirable for the Divine Presence to dwell amidst the children of Israel, since His presence brings blessing to all who dwell in the camp and protects them. No unclean person, just as no unclean animal, may enter the Tabernacle. Also the camp surrounding the Tabernacle must maintain a certain degree of purity, and the Israelites dwelling the in the camp must maintain a degree of purity. This can be deduced from the characteristics of the impure.
Impurity stems, firstly, from contact with a corpse.
Likewise, it stems, secondly, from a leper, a live person who has lost some of his flesh and who appears to be at death's door. Thus impurity is associated with death, while purity is associated with life. This is water that is closest to its condition at the time of Creation. That which promotes creation and life is associated with purification, and that which is detrimental to creation and life is associated with impurity. In other words, life and creation represent the will of G-d, whereas death and degeneration are contrary to His will.