Our parasha finishes with laws of tumah that come upon people, some affecting men and some affecting women, due to discharges from their body. The halachot discussed focus on what makes one tamei for how long, when and how one becomes tahor again, and what korbanot he brings in this context. The following pasuk (Vayikra 15:31) seems to be the beginning of the general p’sukim of summarization: "You shall separate Bnei Yisrael from their impurity, and they shall not die in their impurity while contaminating My sanctum that is in their midst." Chazal explain that this commandment of separation is to not enter the Mikdash in one of several possible states of tumah (see Sifra in the beginning of Tazria).
It is strange structurally for the Torah to insert, at the point of summary, a new halacha of not entering the Mikdash, when this topic is dealt with elsewhere (including Bamidbar 5:3) but not here. It is also hard to pinpoint the meaning of the phrase "separate Bnei Yisrael from their impurity." If this halacha instructs not to enter the Mikdash in that state, it should say to separate from the sacred while tamei, not separate from the tamei. It is difficult to say that it means that the pure should stay away from the impure because neither the text nor the Torah sheb’al peh on it offers such an indication.
Turning to Bamidbar 5, where the positive and negative commandments of not entering the Mikdash while tamei appear (see Sefer Hachinuch #362, #363), the Torah says, "Send out of the encampment" a variety of people who are tamei. However, Chazal explain that they do not have to leave the main encampment, just the area of the Mikdash. This too is difficult. Since people do not live in that area, they do not need to be sent away but rather should be instructed not to approach the sacred area.
We can suggest an answer to all these questions with the help of the Sifra on our original pasuk. Chazal expound on the words "My sanctum that is in their midst" that "even though they are impure, My Divine Presence is in their midst." If that is the case, then the problematic confrontation between the impure and the sacred exists even when the tamei person remains where he is. On a practical basis, there is ostensibly little the person can do. He can’t run away from himself, and he cannot tell the Divine Presence not to approach when he is tamei.
Thus, the p’sukim write the halachot as if the tamei was to be sent away from his home (as hinted in Bamidbar 5) and stay away from the tumah in his own midst (as hinted in Vayikra 15). Practically, a person is to stay away from especially holy places. He is also to use the systems of purification spelled out previously in our parasha which "separates himself" from his own tumah. Not only does this save him from mistakenly going where he is halachically forbidden, but also removes the spiritually unnatural situation of "hosting" the Divine Presence while in a state of tumah.
We should always view ourselves as striving for purity and realizing our potential for sanctity and connection with the Divine Presence. Even if there are few operative halachot of tumah in our days, our mindset should be one of people connected to these two values.