How would you encourage a Christian to resist sin while knowing that God will ultimately work it for their good?
That's really a good question.
Very practically, the devil and our own sin can incline us to use the sovereignty of God to justify complicity in sin. And it's at this point that we need to have a strong commitment to the authority of the Bible and the authority of God telling us how to live with the truth that he has revealed to us.
So many of us learn a fact, like "God is sovereign" or "God loves me" or "God hates sin," and we start spinning implications out of our brain, some of which aren't biblical!
They look rational. They look like they should be believed. "Well, if God is sovereign, then he is responsible for evil. Therefore we can't be responsible. Therefore let us sin that grace may abound," blah blah blah, and it's all unbiblical!
If we're going to latch on to big truths like the sovereignty of God, we've got to latch on to them the way God ordains for us to latch on to them. We've got to latch on to them biblically. That is, we have to see them in connection with all the other biblical truths.
Among those biblical truths is Paul contemplating the thought in Romans 3 and 6, "Shall we sin that grace may abound?" He just said in Romans 5:21 that where sin abounded, grace much more abounded. And here goes somebody with their logic: "Cool! I'll just make grace abound everywhere! I'll just click on as much pornography as I can, and commit as much fornication as I can, and steal as much as I can, and be as greedy as I can. Praise God's grace!"
And Paul answers that in chapter 3 that those people deserve to be accursed. And he says in chapter 6, "Shall we sin that grace may abound? God forbid! For how can you who died still live in it?"
Now there's a truth as important as the truth of God's sovereignty.
Christian, you're dead. You've got to come to terms with what that means. You can't just say, "Well God is sovereign, therefore all my sins are his doing. Therefore I can sin." No! Be biblical. Think God's thoughts. This is complex. Don't depend on your own brain. Depend on God's brain. And God says, "Dead people don't sin" (Romans 6:3).
So you need to figure out what it means to be dead. And put to death what is earthly in you. "If we live according to the flesh, we will die. If we, by the Spirit, put to death the deeds of the body, we will live." That's a truth as big as the truth of God's sovereignty. You can't throw that out and just go do your own logical thing.
So my answer is, Be biblical. We're working here with infinite realities that our brains are not capable of managing on our own. You can't learn one truth from God and then manage it with your brain. You have to constantly submit every thought that you have about God to other thoughts about God so that God manages your brain. Otherwise you will take a truth and distort it in some sinful way.
This is really big. Bottom line: be thoroughly biblical. Test everything by the Bible.