The precise boundary as to what constitutes walking or not walking, or what constitutes living a given lifestyle and not living that lifestyle, cannot be defined. The terms inherently disallow applying such precision. A person's walk or lifestyle is only evident in the big picture. And deviations from the norm can only confidently be spoken of in the extremes.
Let me give you an example. Paul says, "Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor male prostitutes nor homosexual offenders nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God." 1Cor 6:9,10 Let's take for example a drunkard. What constitutes being a drunkard? What I conjure up in my mind is a drunken bump lying in a gutter grasping a bottle of booze. But what about a man who likes to take a little wine with his dinner, and perhaps from time to time takes a little more than he should. Where is the boundary which defines what drunkenness is and what it isn't? Or what of one who may have gotten drunk one time, but normally doesn't touch the stuff at all?
The words "walk" or "lifestyle" don't conjure up point in time events. Nor do they conjure up sort of boundary conditions. Yet it is interesting above that Paul speaks confidently saying that such people as those characterized in 1Cor 6:9,10 will not inherit the kingdom of God. And so also John speaks confidently of the destiny of those walking in the light and those walking in darkness. "He who does what is right is righteous, just as he is righteous. He who does what is sinful is of the devil." 1John 3:7,8 And he even gives a particular case in 1John 2:19 saying, "They went out from us, but they did not really belong to us. or if they had belonged to us, they would have remained with us; but their going showed that none of them belonged to us."
It seems to me that what they are referring to is extreme behavior. It's like the parable of the wheat and tares of Matthew 13. It may be difficult to distinguish between immature Christians and non-Christians. But they are easier to distinguish as they mature in their behavior. Children of the devil will become evident, as will the children of God.
Paul speaks of the Thessalonians saying, "we know, brothers loved by God, that he has chosen you ...", but based this confidence upon the kind of reception the Thessalonians gave them and the Word and their continued obedience inspite of persecution.
But in contrast in view of the problems of the Corinthian church Paul writes to the Corinthians, "Examine yourselves to see whether you are in the faith; test yourselves. Do you not realize that Christ Jesus is in you— unless, of course, you fail the test?"2Cor 13:5
You might have read my page on "How Can You Be Sure of Your Salvation Status?" http://www.bcbsr.com/topics/certain.html There I elaborate upon this whole issue to a degree. I also mention there that one's assurance of salvation should be based upon the degree to which such a person behaves as a child of God. Thus even given Eternal Security, one's feeling of assurance of salvation was meant to be a relative rather than an absolute thing.
If a person is asking himself the question as to how unChristian his behavior could be before he should reckon himself unsaved, or at what point can we say that our sin has become a "lifestyle", God does not provide the answer in the Bible as to what the boundary is. He is purposely vague on this issue in order to scare the hell out of those who like to hang around the fence. He wants us to be far away from that fence. In order to live the Christian life is the answer to that question really necessary? No it's not, because those born of God have no intention of testing that boundary. We want to move on. If God told us exactly how much sin he would tolerate, human nature would drive us to that limit. But keeping it vague hinders our human nature from doing that. It's part of walking in the fear of God. For "if you call on the Father, who without partiality judges according to each one’s work, conduct yourselves throughout the time of your stay here in fear." 1Peter 1:17 Let us therefore be extreme Christians, as the apostles and many of the early Christians. If we don't live up, then yes, let us fear. For "'The Lord will judge his people.' It is a dreadful thing to fall into the hands of the living God." Heb 10:30,31
But then this still begs the question. For even if extreme behavior is used to measure lifestyle, what constitutes extreme behavior? Where is the boundary between extreme and non-extreme behavior? It's really not a boundary. It's a gradient. While salvation status is a boundary, behavior is a gradient. Consider in the Christian life the difference between justification and sanctification. Justification is a boundary, and a point in time event. Either a person's sins are forgiven or they are not forgiven. But sanctification is a gradient. It's a process. It takes time. The degree of Christlikeness of one's behavior and attitudes is relative, progessive. It's only when we are glorified that it will be absolute, when we are transformed.
But even given the fact that "lifestyle" is non-specific, there are times when we are called to judge lifestyle, such as in 1Cor 5:11"I am writing you that you must not associate with anyone who calls himself a brother but is sexually immoral or greedy, an idolater or a slanderer, a drunkard or a swindler. With such a man do not even eat." OK let's say now I have to judge a person's greediness. How greedy does a person have to be before I characterize his lifestyle as being "greedy." Where is the church supposed to draw the boundary in order to carry out this command? Trying to figure that out in any particular case is a matter of discernment which is a part of walking in the Spirit, and which is not the same as legalistically specifying the exact boundary for all cases.
Vaguely and Non-Specifically Yours,