And yet we are required to prove all things in order to hold fast to that which is good. Part of sanctification is judging what is good and doing that. Since we can prove what is good, we can know what is good. How do we know it? What do we prove it with? We use the Bible. But is that all we use? For instance, when we judge language, do we use only the Bible for determining what is good speech? No. The Bible itself assumes that we can know what are good words. We can know what filthy communication is. God says we know, so we do. This is where what we call discernment comes in. We must discern what is good and then do that.
Some of what is good is plainly stated in the Bible. We do not worship idols. We do not bear false witness. We do not murder. We do not steal. Other practices must be judged based on biblical principles. Every decision is not relegated only to what is wrong and right. We've also got to decide based on what is best. We do not love God, our affections do not please Him, without what is excellent.
Paul spent five chapters, 1 Corinthians 6:1-11:1, dealing with the Corinthian church about how to approach non-scriptural issues. A prominent one was eating meat offered unto idols. Was it good to do that? No, but not because there was a verse that said, "Thou shalt not eat meat offered unto idols." Later in Revelation 2, Jesus said He was against it, so it was a settled wrong thing to do in 90, but Paul was taking them through the thinking process about 40 years before. All together, we can see that things can be not good to do that the Bible does not explicitly forbid. How do we determine those? We have to use principles, some of which Paul provides in those five chapters. There are others all over the New Testament.
How do you know you're doing what's good from principles? We can see today that this can be a problem. People are more interested in doing what they want, not in pleasing God. Jesus talked about how serious it was to cause one of these little ones to stumble, so serious that you would better to tie a mammoth, heavy rock around your neck and cast yourself into deep water, than to do that. Very serious. Since the gospels and the epistles say we can know these things and judge these things, then it means that we can. So to start, believe that you can know what is good even if the Bible doesn't make a plain statement about what it is.
Understanding that you can discern using the Bible, get the principles down. Here are a few. Be not conformed to this world (the spirit of the age). Make no provision for the flesh. Abstain from fleshly lusts. Some of the principles are not even stated explicitly. You've got to glean some from an entire passage like 1 Corinthians 10:19-20, an association principle. It is not good even to associate with certain practices, which one would be eating the meat offered to idols.
Where does the conscience come in? The conscience is nothing but a warning device, like the radar on an airplane. It is informed by a law or the law written in your heart. That law might be good. It might not be. Your conscience can be harmed when you don't listen to it. Even when it is misinformed by faulty instruction, the conscience should still perform its function to protect its operation. For instance, someone may grow up being taught that it is wrong to play games with dice. Even if it isn't wrong to play with dice, the person shouldn't play with dice if his conscience tells him not to do that. If he goes ahead and plays, he'll harm his conscience. That's another principle. Don't hurt your or someone else's conscience. When the conscience warns about something that is good or bad, it won't function right if it has been ruined already.
Does the conscience itself teach virtue? No. The conscience only warns. It doesn't inform. So someone who talks about "hitching his virtue to someone else's conscience" doesn't understand the conscience. A conscience should be informed by what is true and good and beautiful.
After someone knows the principles well, how does he insure he will put them into practice well (good)? There are many factors here. He should look at how it has been practiced in history. The Holy Spirit informs by the regular practice of believers through centuries. He should consider his church, the temple of the Holy Spirit. He should follow godly leaders. That would be sort of like being "good on someone else's nickel" that I read somewhere recently. Is that scriptural? Sure. It's what Paul ended the five chapters with in 11:1, "Be ye followers (imitators) of me, even as I also am of Christ." It's a good thing to copy other, more experienced, Christians. Paul even commanded it here. You're not a lesser person for having done so, even though others (who ironically want people to imitate them) might say you are not.
Recently here, I asked questions about soccer shorts and modesty of women. Are soccer shorts on women categorically a non-scriptural issue? Are there no objective standards of nudity or nakedness in the Bible? Is that how Christians have practiced in this realm? I've read a lot about this, and the answer is, "No." Women shouldn't be showing their breasts and thighs. Does it make it right if they are ignorant of it through decades of conforming to a worldly philosophy? No. Sure, they might not be wearing the shorts to rebel. But they're still wrong. I might not put on my seatbelt because I hate the law, but I'll still go through the windshield, no matter what my motive.
A good passage to consider on this, that is 100% appropriate, is the ark narrative in 1 Chronicles. After David took the throne, he wanted to bring the ark back to Jerusalem. Was that good? Yes. It was good. He put it on an oxcart. Did that mean he was a rebel against God? No. David wasn't a rebel against God. But God still killed Uzzah when he touched the ark. God did not approve of carrying the ark on a cart. It was not good.
Are women trying to be rebellious and androgynous and feminist by wearing soccer shorts? I don't think so. Is every child being rebellious because he screams like a wild banshee for candy at the supermarket checkout? It really does look rebellious to me. It doesn't look good. It isn't good. Just because the child doesn't know any better doesn't mean that it is good behavior. Same with the women in the soccer shorts. They don't get a pass from God for wearing them, just like David did not get a pass for carrying the ark on a cart.
Think about it.