The short answer is that a Christian can sin just as badly as a non-Christian person. However, many differences exist in the life of a Christian that do not exist in the life of a non-Christian.
How much can a Christian sin?
A Christian has the Holy Spirit living within them. When a Christian sins, there is a conviction from God's Spirit. This conviction should lead to repentance rather than repeating sins without remorse.
A Christian has spiritual power to overcome sin. Though every Christian will continue to sin until being made new in heaven, a Christian empowered by God's Spirit can certainly make progress in living a more holy life than before.
A Christian will naturally desire to do what is right even when his or her actions are wrong. For example, Paul wrote, "For I do not do the good I want, but the evil I do not want is what I keep on doing. Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me" (Romans 7:19-20).
A growing Christian will become increasingly aware of how sinful his or her actions are before God. Again, the apostle Paul serves as an excellent example. Considered the greatest missionary of the early church, one of his final letters notes, "Christ Jesus came into the world to save sinners, of whom I am the foremost. But I received mercy for this reason, that in me, as the foremost, Jesus Christ might display his perfect patience as an example to those who were to believe in him for eternal life" (1 Timothy 1:15-16).
Romans 8:37-39 make it clear that nothing can separate us from God's love. First John 5:13 shares we can know for certain we have eternal life. However, these four areas should also cause us to evaluate our spiritual lives. If you do not sense God's conviction of sin, do not find yourself making some progress to overcome sin, do not desire to do what is right, or do not see yourself as sinful, it is possible you may not be a true follower of Christ.
In Matthew 7:22-23, Jesus taught, "On that day many will say to me, 'Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?' And then will I declare to them, 'I never knew you; depart from me, you workers of lawlessness.'" Our salvation is not based on our works. In this example, Jesus turned away those who prophesied and cast out demons, considered two of the greatest spiritual activities a person could perform. Instead, salvation is based on grace through faith in Christ (Ephesians 2:8-9). This salvation will result in a changed life in which one desires to live according to God's ways (James 1:22).
Are all sins equal?
The consequences of sin - What are they?
Does my private, personal sin affect others?
Does everyone inherit sin from Adam and Eve?
The sin nature - What is it?
Truth about Sin