We can learn from the curses of the Tokheha what it means to truly walk with God, and to fully internalize that there is something greater than ourselves.
For 25 chapters, the book of Vayikra has described what it takes to make holiness real in this world. Chapter 26 gives us the antithesis, the dark side. The structures of seven which formed the foundations of holiness- Shabbat, Shavuot, Shemita, Yovel- now form outlines of increasing suffering. The animals we were to use to bring us closer now attack us. The diseases which served as spiritual warning signals, accompanied by rituals that brought the sufferer back into the camp, now only bring affliction and exile.
What would bring all this on? It's the difference of one letter; substituting last chapter's mindset of geula (gimmel-aleph-lamed) with this chapter's refrain of gi'ul (gimmel-ayin-lamed). Rashi explains that gi'ul means the expulsion of one thing from that in which it was absorbed. Sounds gross, but what does it mean?
The rebellion against the holiness of Vayikra is, at the root, a refusal to accept the reality, and the regularity, of Godliness within our midst- "and I will place my dwelling place among you, and my soul will not expel you (lo tig'al nafshi), and I will walk among you."
Why would someone reject this?
Instead of allowing God to walk within our midst with regularity, we walk with God 'be'keri'- occasionally. This isn't the outright rejection of God; even while we are rejecting His covenant, we are still offering sacrifices (see verse 31). It's even uglier. When it suits our own needs, we'll walk with God. Instead of fully internalizing God's presence, we externalize it, we turn it into something outside ourselves that we can use when it suits us, and ignore when it doesn't.
The ultimate expression of this is the inability to maintain the laws of Shemita. This stems from the inability to refrain, to relinquish control, to admit we are not the true owners, we are not the measure of all things. Shemita demands that we realize there is something greater than ourselves, and, indeed, this can be seen as an overarching theme of the Mishkan, and of the book of Vayikra. The expulsion (gi'ul) of God from our midst ultimately comes down to one thing- hubris. It is an arrogance which blinds people from recognizing their mistakes, even when they are suffering increasingly from them. It is an arrogance which can only lead in the end to our own expulsion.