Why do Christians do good works and do what they do? Some say that it's just for reward and that it's possible to be barren by God's grace. Others say that it's because if Christians don't continue doing good works they can lose their salvation. Both of them are lies straight from the pit of Hell because if you've got God's grace, you're going to change. Do you know what changes the worst of sinner to a sanctified saint? It's never the flesh because as Romans 7:18 and Galatians 5:19 all condemn the works of the flesh. Man is born a sinner so there's only God's grace that really helps them overcome their sin.
The Apostle Paul said in 1 Corinthians 15:10 that it's by God's grace that he is what he is. The Christian cry has always been by Scripture alone, faith alone, by grace alone, in Christ alone and glory to God alone. The whole life of the Christian is built on the Word of God which declares that from salvation to sanctification it has always been by grace through faith. Ephesians 2:8-10 and Titus 2:11-14 declare that that when a man is saved, they're going to be taught good works by the grace of God and not of themselves. When a person is saved by God's grace it creates that attitude of gratitude, it creates that growing hatred for sin and as 1 Corinthians 6:11 declares that such people were saved from their lifestyles of sin after they got saved, not before.
Why do Christians have no right to boast about my power against sin? Because that power against sin is by the grace of God, I didn't really have it until I became a partaker of God's grace by faith in His Son, the Lord Jesus Christ. Hebrews 9:12 declares the conscience is to be purged by the blood of Jesus from dead works to serve the living God. When that person claims to have God's grace but doesn't have any change at all then that person's salvation is as spurious as the other person who claims good works are needed to maintain salvation or the idea that God saves a person then leaves them on their own. Such ideas are all misguided and heretical both on their way to Hellfire.