How do I know if something is a sin?

Question 11088

Discerning sin is one of the ordinary tasks of the Christian life, and it is a good deal harder than the lists suggest. Scripture names a great many things plainly, and then leaves us with hundreds of daily decisions it never mentions: this job, that programme, this investment, that friendship, this way of spending a Saturday.

So how do you tell? Not by instinct alone, and not by asking whether other Christians do it. Scripture gives us a set of tests that work together, and learning to apply them is a large part of what it means to grow up.

Discerning Sin Starts With What Scripture Says Plainly

Before any subtlety, there is the obvious. Sin is lawlessness (1 John 3:4), a failure to conform to the character of God as He has revealed it. Where Scripture names something directly, discerning sin requires no ingenuity at all. It requires obedience.

The New Testament contains extensive descriptions of what belongs to the old life and what belongs to the new. Galatians 5:19-21 sets out the works of the flesh, from sexual immorality and idolatry to enmity, jealousy, fits of anger, rivalries and envy. Notice how many of those are respectable sins that rarely get preached about.

A surprising amount of the moral confusion in the church would dissolve if believers simply read these passages and took them at face value. Discerning sin becomes complicated only after the plain material has been absorbed, and most of us are still working on that.

What Continues Now That the Mosaic Law Has Ended

A word is needed here, because people often reach for the Ten Commandments as the standard. The believer is not under the Mosaic covenant, which came as a covenantal package to Israel and ended as one (Romans 10:4; Galatians 3:23-26; Hebrews 8:13). That is not a licence for looseness.

What continues is the moral character of God, which predates Sinai and is now expressed through Jesus, the apostolic teaching of the New Testament, and the Spirit who writes God’s character on the heart. Nine of the Decalogue’s provisions are reissued in the New Testament, often with greater depth than Sinai required. I have set this out in my answer on the role of the law for Christians.

So discerning sin is not a matter of consulting an external code and finding the relevant clause. It is a matter of knowing the God whose character defines the standard, which is why growth in Scripture and growth in discernment tend to arrive together.

The Conscience Test

Paul writes that whatever does not proceed from faith is sin (Romans 14:23). If you cannot do it with a clear conscience before God, then for you it is sin, even if the thing itself is neutral and another believer does it freely.

The conscience, suneidesis, is a genuine gift and an imperfect instrument. It can be over sensitive, condemning where God does not, and it can be seared by repeated violation until it stops signalling at all. It needs educating by Scripture rather than obeying blindly.

Still, a conscience that hesitates is telling you something. The rule I give people is straightforward: if you are not sure, do not do it yet. Wait, study, ask. Discerning sin rarely suffers from a delay, and acting against an uncertain conscience trains you to ignore it.

The Enslavement Test

All things are lawful for me, but not all things are helpful; all things are lawful for me, but I will not be dominated by anything (1 Corinthians 6:12). Ask whether the thing has any grip on you. Could you stop tomorrow without distress? Have you tried?

This test catches a whole category that no list would identify: the box set that eats the evenings, the phone reached for at every idle moment, the shopping that soothes something. None of these is named in Scripture, and any of them can become a master.

Enslavement is one of the clearest signals in discerning sin, because idolatry is the underlying category and idolatry is always about what governs. If the answer to could you give it up is a flash of resistance, you have learned something.

The Love Test

Not all things build up, Paul adds. Romans 14 and 1 Corinthians 8 both deal at length with actions that are legitimate in themselves but damaging to somebody else, and in both cases Paul asks the strong believer to give ground for the sake of the weaker.

So the question is not only what does this do to me but what does this do to others. Discerning sin has a social dimension that individualistic Christianity tends to miss. It is possible to be technically within your rights and genuinely wrong.

This cuts both ways, incidentally. Paul refuses to let the weaker brother become a tyrant who dictates the conscience of the whole church. Love yields; it does not legislate. The translators’ notes at the NET Bible on Romans 14 set out the tensions in that chapter carefully.

The Glory Test

So, whether you eat or drink, or whatever you do, do all to the glory of God (1 Corinthians 10:31). This is the widest of the tests and in some ways the most searching, because it does not ask whether an action is permitted but what it is for.

Can you do this thing and thank God for it honestly? Gratitude is a remarkably good detector. Most of us find that the things we are uneasy about are precisely the things we would not naturally give thanks for, and the awkwardness of trying is itself the answer.

Colossians 3:17 puts it in terms of doing everything in the name of the Lord Jesus. Discerning sin from this angle means asking whether you could carry out the action as His representative, which is a different and more useful question than whether you could get away with it.

The Direction Test

Finally, ask where this is taking you. Sin rarely announces itself at the start; it accumulates. The question is not only whether a single instance is wrong but whether the pattern is moving you towards God or away from Him, towards freedom or towards captivity.

Hebrews 12:1 speaks of laying aside every weight and the sin that clings so closely. Weights are not necessarily sins. They are things that slow you down, and a serious runner discards them regardless of whether they are technically forbidden.

This is why discerning sin is a skill rather than a lookup. The mature have their powers of discernment trained by constant practice to distinguish good from evil (Hebrews 5:14). Training implies repetition, mistakes and gradual improvement.

When You Still Cannot Tell

Ask someone. Not someone who will tell you what you want to hear, but a believer who knows Scripture and knows you and is willing to be uncomfortable. Most of us are poor judges in our own case, and the church exists partly to supply what we lack alone.

Give it time. Sleep on it. Pray specifically rather than generally. And be willing to conclude that the answer is no, because a person who only ever seeks counsel until he gets permission is not actually discerning anything.

If after all of that it remains genuinely unclear, act in faith and leave the outcome with God. He is not waiting to catch you out on a judgement call made honestly with the light you had.

Discerning Sin in a Complicated World

Some questions are harder than the tests alone can settle, because the moral weight is spread across systems rather than sitting in a single act. Where your pension is invested, what the company you work for does elsewhere, how the cheap product on the shelf came to be cheap.

Scripture does not give a rule for these, and anyone who claims otherwise is inventing. What it gives is a direction of travel: love of neighbour, care for the poor, honesty in dealing, and a refusal to profit knowingly from another’s harm. Discerning sin at this level means taking responsibility for what you can actually know and change, and not pretending to a purity nobody has.

I would rather a Christian made one honest change than paralysed himself calculating an impossible total. Do what is in front of you, and let a tender conscience keep working on the rest.

So, now what?

Take the one thing you have been uneasy about and run it through the tests deliberately. Does Scripture speak to it? Can I do it in faith? Does it have a grip on me? Does it harm anyone? Can I thank God for it? Where is it taking me?

Then act on the answer rather than filing it. Discerning sin is worthless as an exercise if the conclusion changes nothing. What has your conscience been raising with you that you have been managing to ignore?

But solid food is for the mature, for those who have their powers of discernment trained by constant practice to distinguish good from evil.

Hebrews 5:14, ESV