I'm just a tool
Part of the effect of today's humanistic mindset is that we evaluate ourselves too highly. We compare ourselves to the world around us, and seem to be so far ahead of the rest of creation. Part of our pride likely lies in our perceived free will - it seems to be what distinguishes us from the animal world.
But what do we see here? In this passage, Paul says that we are either instruments (or tools) for sin or for God. This dichotomous thinking isn't just found here. Other passages talk about only having one master, and of being either slaves to sin or slaves to righteousness. But Paul ups the ante here. He argues that we're not just servants who pick a master, or slaves who are controlled by an owner. Rather, we are akin to mindless tools!
To be sure, the onus is on us in terms of which hands we will place ourselves in. But once we place ourselves in those hands, we tend to be freely wielded (by either sin or God). Don't feel like digging in the garbage? Too bad - the tool-user says it's time to dig in the garbage. Don't think you know how to fix the leaky faucet? Well, the tool-user is going to use you anyway.
In the positive, this is exciting - if we allow God to pick us up and use us, there's no telling what God may end up doing with us - we just know it's going to be good, exciting, and for His glory. In the negative, this is frightening. As simple tools, if we allow ourselves to be picked up by sin, we're going to be used by sin, whether we like it or not. And it's shockingly hard to get out of sin's grip.
We (I) need to come off of this humanistic high that says I'm a completely free agent in this universe. No, there are forces much stronger than me out there. I was made to be a tool for God and God alone. Unfortunately, my "tool nature" makes me susceptible to frequent use by sin. It's only when I consistently get into the hands of God that I will consistently achieve my purpose, as a tool of God.