A question on the Perseverance of the Saints: How much can you sin before you are no longer a Christian?
The answer is found in 1 John 3:9:
No one born of God makes a practice of sinning, for God's seed abides in him, and he cannot keep on sinning because he has been born of God. (ESV)
Notice the phrase "born of God." This refers to someone who is truly a Christian—someone who has genuinely been regenerated by God.
John teaches that no one who has been born of God makes a practice of sinning. In other words, a genuine Christian will not be characterized by habitual, unrepentant sin.
This doesn't mean Christians never sin. Rather, it means that something changes when a person is saved by Jesus.
You begin to desire holiness. You want to be like Christ. You want your life to be conformed to His image, and you want to please God with the way you live.
That's part of what comes with being saved by Jesus.
A Christian receives forgiveness from sin and wants to turn away from sin.
This is what it means to not make a practice of sinning. Sin is no longer something you want to embrace as your way of life. Instead, you desire to pursue holiness and become more like Jesus.
So, returning to our original question: How much can you sin before you are no longer a Christian?
Rather than looking for how much sin you can get away with, the Christian should desire to live a life that pleases God.
That desire doesn't earn salvation. It is evidence of the transforming work God has already begun in you.