Parsha Kedoshim, Leviticus 19 - 20, opens and closes with a command from God that His people be holy because He is holy. In between is a series of social and moral ordinances which many commentators interpret as components of holiness. While these ordinances are surely characteristic of holiness, I believe that to so view them misses a larger point.2
To see what's going on, we must begin with the end of parsha Acharei Mot, Lev 18:24, which warns that if Israel defiles herself, the land will vomit her out as it did the prior inhabitants. With that slight expansion, we see the following structure to Torah portion Kedoshim:
The structure highlights the importance of the Land of Israel and its active role in determining who is allowed to live there. To see how this works, consider Lev 18:24-28:
Do not make yourselves unclean by any of these things, for by all these the nations I am driving out before you have become unclean, and the land became unclean, so that I punished its iniquity, and the land vomited out its inhabitants. But you shall keep my statutes and my rules and do none of these abominations, either the native or the stranger who sojourns among you (for the people of the land, who were before you, did all of these abominations, so that the land became unclean), lest the land vomit you out when you make it unclean, as it vomited out the nation that was before you.
Notice the sequence:
Thus, the Land has a special, active role in deciding who will live therein and in the process of exile for those who do not measure up. Why? Consider the history. When God began the process of humanity's restoration and redemption - which is still incomplete - He chose Abram to father the people through whom He would work. Genesis makes clear that the first step after Abram's selection was to move him to the Land. Later, when Abraham's sons sent back to his family in Haran to get wives, they then returned to the Land. Israel has, at various times, been exiled from the Land, but they have always been brought back.
Another way to say the same thing is that the Land of Israel is hostile to natural man. When Israel behaves in a Godly fashion, it is secure in the land. When she behaves like the rest of humanity, the land casts her out.
So we can theorize that both the land and the people are necessary for God's plan. If only the people were needed, there would have been no need for Abram to move. If only the land were needed, then it would not really matter who lived there; God could do what was needed with anyone.
If we consider the purpose for which man was created, we may begin to understand what is going on. We were created by God to be His agents in tending the Earth. We were also created to be in fellowship with Him as we carried out this function.
2This line of thought was suggested by Growing Pains by Rabbi Noson Weisz