Do you have trouble in some “grey areas” things where some believe it is sin while others don’t? How can we know when something’s sin or not?
There are many things in the Bible that are clearly black and white, meaning, things like sexual immorality is sinful. There’s no question that adultery and fornication is sin. The Bible spells that out in clear language. The Apostle Paul writes that “the works of the flesh are evident: sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these,” but then Paul says, “I warn you, as I warned you before, that those who do such things will not inherit the kingdom of God” (Gal 5:19-21). These are so obviously sinful that we don’t have to ask if they’re sin or not. It doesn’t take a lot of study and you don’t have to be a theologian to know that those who practice these things are sinning. Undoubtedly, it is sin to steal, murder, and lie, but what about gray area things? What if some people do things that you think are sin, but not for them? And, how can you know whether its sin or not for you?
Benefit of the Doubt
When you’re unsure about whether something is sin or not, I think it’s best to avoid doing it altogether. If you’re not sure, that may be a sign that it’s wrong, otherwise your conscience wouldn’t even be bringing it up. If it doesn’t trouble your conscience but it still might cause your brother or sister to stumble, then its best not do it at all…even if you think it’s not sin. Some Christians do things that you feel are wrong, but we must remember that they might be overcoming things a bit slower, or they might have other issues to work on before dealing with the thing that bothers you. And, to them it may not even be sinful. If it’s an area you’re not sure of, it’s best to remain silent. Let the Holy Spirit work in their heart to convict them that its sin. That’s His job, not ours. Paul says that “the works of the flesh are evident” (Gal 9:19), but that doesn’t mean everyone who bears fleshly fruit is lost. Everyone’s journey into the kingdom is different. It will not look like yours and mine, but obviously, when there is doubt, it’s time to leave it out. If you’re not sure about doing something, then don’t do it. You won’t ever regret not doing something because you did it out of a sincere desire to not sin and live in obedience to God’s commands.
We’ve read about the obvious sins like “sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these” (Gal 5:19-21a), so there’s no doubting whether these things are sin or not, but some people smoke, others drink alcohol, and some even gamble, so are these things sin or not? Although drinking might not be sin for you, drunkenness would be. A lot of famous Christians smoked, like C.S. Lewis (a pipe) and Charles Spurgeon (cigars), so for me to come up to either of these great men and tell them, “You’re sinning” would be wrong. To be fair, Charles Spurgeon quit smoking, but only after he saw his picture in a newspaper ad that was selling cigars! AHe was convicted by that and quit, so if they are not bothered by it, should we? That’s not the case with sexual immorality. That is something that is positively sin and we should immediately go to our brother or sister about that; first privately, and if that doesn’t work, go with a friend, and if that still doesn’t work, bring it up before the church (Matt 18:15-20), but only as a last resort, so if you see a fellow brother or sister drinking a beer at a bar-b-q, we had better hold our tongue because it may not be sin for them. I don’t drink, but that’s me, and I’m not them.
Being Fully Convinced
James wrote, “So whoever knows the right thing to do and fails to do it, for him it is sin” (James 4:17), so there are sins of commission, but also sins of omission. It all goes back to our conscience and the conviction of the Holy Spirit. The Apostle Paul says that “whoever has doubts is condemned if he eats, because the eating is not from faith. For whatever does not proceed from faith is sin” (Rom 14:23), but “Each one should be fully convinced in his own mind” (Rom 14:5). I cannot let my “fully convinced mind” that tell me something is sin for me but also for everyone else. The obvious sins, yes, (Gal 5:19-22), but not those areas not specifically mentioned in the Bible. The Bible gives us general principles that we can apply to every grey area, however, some things that we think are sin may not be specifically mentioned in the Bible. If they are not specifically addressed in the Bible, we should not act as if they are and try to be the “church police.” The Holy Spirit is much better at convicting people of sin than we are, and the regenerating work of the Spirit is more effective than human arguments. If we are convinced that something in a grey area is sin, then its sin to us, however we don’t have the right to confront a fellow believer, because it may not be sin to them. Paul wants Christians to “stop passing judgment on one another. Instead, make up your mind not to put any stumbling block or obstacle in the way of a brother or sister. I am convinced, being fully persuaded in the Lord Jesus, that nothing is unclean in itself. But if anyone regards something as unclean, then for that person it is unclean” (Rom 14:13-14).
One general rule that works well in regards to whether something is sin or not is if you don’t feel 100% certain about it, don’t do it. If there are doubts, do without. I would not want to go against my conscience. The Apostle Paul talks about those whose go against their consciences’ and that “the Spirit expressly says that in later times some will depart from the faith by devoting themselves to deceitful spirits and teachings of demons, through the insincerity of liars whose consciences are seared” (1 Tim 4:1-2). Like a callous on your hand eventually loses sensitivity to feeling, so a sin-seared conscience will have no conviction when they sin. This means that sin will be free to abound since they are suppressing the knowledge of God and stilling the voice of the Holy Spirit (Rom 1:18-20).
The flesh is like an accelerator in a car, but the Spirit of God acts like a brake. He helps warn us and tells us when it’s time to slow down or turn to avoid hazards, however, if you ignore the brake, the speed will go up, just as sin will increase where the Spirit’s voice is suppressed. The Holy Spirit will help us discern whether something is sin or not, but only for us and not for others. Regularly reading the Word of God will help as well, so if the sins are clearly marked out in Scripture (i.e. sexual immorality; Gal 5:17-21), we have the obligation to go to our brother or sister (Matt 18:15-20). Otherwise, “Each one should be fully convinced in his own mind” (Rom 14:5).
Here is some related reading for you: Right Verses Wrong: How to Answer this from the Bible 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible : English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.