Dec 21, 2022

How Do I Know If Something Is a Sin?

4 Min Read

If we don’t believe that we are sinners, then we will not have an accurate understanding of our need for a Savior. It is only when we understand that we are sinners that we will flee to Christ for forgiveness of our sin. And in order to understand that we are sinners, we need to know what sin is.

The Scriptures teach us that sin is displeasing to God, and that it merits spiritual death and an eternal judgment (Rom. 6:23; John 8:24). So, it is essential to know what sin is so that we can find a remedy for it in Christ and seek to avoid sin, that we might live a life that is pleasing to God. We cannot do this if we don’t know what sin is and what it is not; if we cannot distinguish between things that are sinful and things that are not.

First, let us consider what sin is not. Sin is not our opinion of what is right and wrong. It is not our own private list: “the filthy five, the nasty nine, the dirty dozen,” etc. It is not as though I can have my list of what I think sin is, and you can have yours. For example, “Adultery is sin, but sex outside of marriage is not sin as long as the two people love each other.” Proverbs 12:15 tells us, “The way of a fool is right in his own eyes . . . ”

Neither is sin defined by preferences: “I don’t like rock music, so rock music is sinful.” or “I don’t like dancing, so it must be sin.” Sin is not a matter of one’s personal preferences, nor is it a matter of societal mores. In other words, sin is not determined by psychological or sociological surveys. Some would say, “As long as the majority of society says something is permissible, then it can’t be sin. So, if abortion is approved by society, it can’t be sin. If all divorce is approved by society, it can’t be sin. If homosexuality is approved by society, it can’t be sin.” However, what is sin and what is not sin is not to be determined by sociological studies or by the majority vote of the population. How then do we determine what sin is?

Sin is defined for us in God’s Word. The Apostle John writes, “Everyone who makes a practice of sinning also practices lawlessness; sin is lawlessness” (1 John 3:4). Sin is defined not in terms of our opinion, or the opinion of others, or in terms of what makes us feel bad, or any other man-made criteria. Sin is defined by God in terms of His Law. Sin is “lawlessness.” (1 John 3:4).

Sin is defined in terms of God’s law because God’s law is a reflection of His holy character.

Sin is defined in terms of God’s law because God’s law is a reflection of His holy character. Note how the law is defined in Romans 7:12, “So the law is holy, and the commandment is holy and righteous and good.” The words used to define the law of God are the same words used to describe the character of God. God is holy, and He requires us as His image bearers to be holy as well. Obedience to God’s holy law defines holy living for the believer and unbeliever alike. Sin is “unloving disobedience” to God’s will as expressed in His holy law and Word. In it, He shows us what He requires and what He forbids.

The Westminster Shorter Catechism, Question 14, asks, “What is sin?” The answer given is, “Sin is any want [lack] of conformity unto, or transgression of, the law of God.” This is probably as good a definition as could be given of what sin is. First, God’s law, anchored in God’s character (Rom. 7:12), is the standard. And second, there are two broad categories of sin. Generally, they are called sins of omission and sins of commission. In other words, we can sin by what we don’t think, say, or do, as well as by what we do think, say, or do. This is what Question 14 means when it says “want of conformity unto,”—that is, when we fail to do what God requires us to do in His law. If God states in His law, “Husbands, love your wives, as Christ loved the church” (Eph. 5:25), and we don’t do it, it is sin. If God commands us to worship Him together with His people and not to forsake the assembly of His people, and we forsake it, it is sin.

And then there are sins of commission as well. This is what Question 14 means when it says “or transgression of”—that is, when we do what God forbids us to do. It is sin when we violate God’s standards of holiness revealed in His law. When God says, “You shall not commit adultery,” and we go ahead and do it anyway, we have sinned. We have transgressed His law by going against it and have crossed over it.

This is why we need to be exposed to the teaching of God’s Word and law. In order for us to understand what God requires of us, to understand the gravity of our sinful condition, to understand our need for the grace and mercy of God in Christ Jesus our Lord, we must know God’s law. The law reveals what is sin in our lives and shows us our need for Christ (Rom. 7:7–11). Those who understand the true nature of sin and define sin as God does say, “I am undone! I am a sinner, condemned, unclean, the chief of sinners!” They can then find forgiveness by God’s grace in Jesus. He is the Lamb of God who takes away sin. As believers in Jesus whose sins have been forgiven, we can know how to pursue a life that is pleasing in His sight by knowing what is sin and what is not, as we read and study the law and Word of God.