R.C. Sproul, a great theologian, lays out in his book Chosen by God that we are born with a sin nature. The reason for this sin nature is that we are under the curse of Original Sin from our first parents Adam and Eve. Before the Fall of Adam and Eve, man was able to sin, but he was also able to not sin. He has the choice between obedience and disobedience. After the Fall of Adam and Eve, the nature of humanity changed. We were now able to sin, and unable not to sin. In other words, we were free to sin with our choices, and at the same time, our freedom is restricted in the sense that we are unable not to sin. We will sin as a result of the Fall of Man. The beauty of the gospel and being a person set free in Christ is that we are no longer obligated to sin. Whoever the Son has set free, he is free indeed. When we are born-again we now go back to our pre-Fall nature: we can sin and we can not sin. The process of holiness is trusting and leaning on Christ more and more to be able to choose not to sin when sin is before us. If we are in Christ, we curse him if we continue to say that you sin because you can't do otherwise. Not so if you are in Christ. Will we still sin? Yes. But make no mistake, we no longer have to sin. Before our rebirth in Christ, we are unable not to sin because of our corrupt hearts, minds, and nature. In heaven, when we finally are glorified and redeemed fully, we will be able not to sin and be unable to sin. So we will not only have the ability to not sin, we will lack the ability to sin. Praise God for that!!
Back to the issue of holiness. Holiness is possible. If you are reborn in Christ, you can be holy, you can choose not to sin. People often talk about how they want God to use them. I hear people ask me all the time, "just pray that God would use me." I don't have a problem praying for that, but here's the deal: God will use you if you are 1. reborn in Christ and 2. living a life of holiness. If you are not doing those things, no need for me to pray. In fact, look at the passage from 2 Timothy 3:20-21
20Now in a great house there are not only vessels of gold and silver but also of wood and clay, some for honorable use, some for dishonorable. 21Therefore, if anyone cleanses himself from what is dishonorable, he will be a vessel for honorable use, set apart as holy, useful to the master of the house, ready for every good work."
The passage shows us that it doesn't matter what kind of vessel it is, as long as the vessel is clean it can be ready for honorable use. If it is clean, it can be set apart, useful to the master, ready for every good work. Paul is saying this: it doesn't matter what your spiritual gift is, your background, your age, etc. what matters in the issue of being used by God is holiness. We must be holy because God is holy. We must quit excusing our sin on our nature when in the rebirth we were given the ability not to sin. We must seek to be holy if we want to be used by God. We should quit praying for God to use us and instead focus on holiness. When we do that, God will wear us out.