Do We Overcome Sin by Our Power or by God's Power?
I think the answer, based on the Bible, is both.
Our own power is not sufficient. We need God's help to overcome. But we must make the effort.
If we think it is only by our power, we deceive ourselves and think that we are self-sufficient. If we think it is only by God's power, we may wait for God to do everything for us and not go all out 100% to do our part, to make the effort. We have to strive with all our might to overcome sin, then trust God to give us the extra help we need to succeed.
God's Spirit gives us the understanding of God's law. God does this by opening our minds to understand the Bible and by helping us see how to apply Bible instruction to the circumstances of our life. Without that help from God, we would be deceived like the world and not understand God's law and its correct application. But we must make the effort. Even then, our effort may not be sufficient to break bad habits, overcome addictions, and put sin out of our lives, but we need to pray for God's help and keep trying with all our might, trusting God to give us the victory in the end.
Here is a quote from my book, Preaching the Gospel:
"I have heard some speakers say that a problem some people have in trying to overcome addictive sins is that they are not able to do it because they are trying to do it by their own power. When I hear this, I am never quite sure what the speaker means. Sometimes the speaker may say that we need to quit trying to overcome sin by our own power. But I find no verse in the Bible that says, 'Don't try to overcome sin by your own power.'
"Certainly we should ask God for help to overcome. But we must also do our part by trying as hard as we can. It is not a matter of doing it by God's power or our own. It is both. God helps us in our trials by giving us power and help in ADDITION to what we are able to do for ourselves. For example, if I am unemployed, I may pray and ask God to help me find a job, but then after praying I should do my part by diligently looking for a job.
"God wants us to make the maximum effort we can. Jesus Christ said, 'If your hand or foot causes you to sin, cut it off and cast it from you. It is better for you to enter into life lame or maimed, rather than having two hands or two feet, to be cast into the everlasting fire. And if your eye causes you to sin, pluck it out and cast it from you. It is better for you to enter into life with one eye, rather than having two eyes, to be cast into hell fire' (Matthew 18:8-9). Jesus is speaking figuratively. He does not want us to physically mutilate or injure our bodies, for the Bible also says, 'Do you not know that you are the temple of God and that the Spirit of God dwells in you? If anyone defiles the temple of God, God will destroy him. For the temple of God is holy, which temple you are' (1 Corinthians 3:16-17). Our bodies belong to God, and we should protect and take care of our health. In the sermon on the mount, Jesus is speaking figuratively to illustrate how great our effort should be to overcome sin, even to the point of giving up things we may love to avoid the temptations of sin. An example of how to apply this might be a person who has a problem with over-drinking giving up alcohol altogether, because trying to drink alcohol in moderation is a temptation for that person to drink in excess.
"When Jacob wrestled with God, God refused to bless him until Jacob proved his willingness to strive with all his might to obtain the blessing, even when in pain (Genesis 32:22-31).
"An example of the balance between our effort and the additional power God gives us can be found in the life of Samson. After he lost his strength because his hair was cut and the Philistines put out his eyes, he was in the temple of the Philistines where they were assembled. 'Then Samson called to the Lord, saying, "O Lord God, remember me, I pray! Strengthen me, I pray, just this once, O God, that I may with one blow take vengeance on the Philistines for my two eyes!" And Samson took hold of the two middle pillars which supported the temple, and he braced himself against them, one on his right and the other on his left. Then Samson said, "Let me die with the Philistines!" And he pushed with all his might, and the temple fell on the lords and all the people who were in it. So the dead that he killed at his death were more than he had killed in his life' (Judges 16:28-30). Note the sequence. First Samson asked God to give him strength. Then he pushed 'with all his might'. He asked God for help, then he made maximum effort to push on the pillars.
"Did Samson do it by God's power or his own strength? I think the answer is, both. Most of the actual physical power came from God, but I don't think God would have supplied that power if Samson was not trying as hard as he could. And part of it was Samson's strength, even if it was only 1%. Samson did his part with whatever strength he had, and God supplied the additional strength that he needed to succeed.
"There may also be a lesson in this for preaching the gospel. As a Church, we need to strive with ALL our might to preach the gospel to the world, and then God can give us the extra help we need to succeed. When God sees that individual members are striving hard to sacrifice to support the preaching of the gospel and the Ezekiel warning to the public out of a motive of love, He can bless us with more power to do so. But if we are only making a half-hearted effort, I think God will help us less until our attitude improves."
Here are links to related sections in Preaching the Gospel:
How to Obtain More of God's Help in Breaking Bad Habits, Chapter 7