The difficulty with the word
sin in the Bible is that sometimes it refers to the sinful nature and sometimes to sinful acts. The average person only thinks it refers to the latter. I sometimes use the picture of the sinful nature is the tree, and sinful acts are the fruit of that tree.
Scripture
One place in Scripture to look is 1 Tim. 1:9.
KJV said:
Knowing this, that the law is not made for a righteous man, but for the lawless and disobedient, for the ungodly and for sinners, for unholy and profane, for murderers of fathers and murderers of mothers, for manslayers,...(1 Tim. 1:9)
We know what the later ones in the list mean but what about the first 6? The way to find out is open a concordance and a dictionary to learn what those words mean. It ends up meaning something like, "Knowing this, that the law is not made for a righteous man [believers], but for those who are without God's law written in their hearts, those neglecting or refusing to obey God, those who are irreverent towards God, those lacking respect or esteem for God and his authority, those who by nature disobey God, the godless and the ungodly,...".
My favorite Scriptural example of the sinful nature is in Deuteronomy chapter 1. God commands the Israelites to go into the land and fight and take the land, but they refuse and stay in the camp. Then they decide to go in and fight but God tells them to stay in the camp. The "sin" ends up being morally neutral. The "sin" is doing the opposite of what God says.
Martin Luther
Martin Luther wrote a book called
Commentary On Romans. In the "
Preface to the Letter of St. Paul to the Romans" he said this about sin.
Preface to the Letter of St. Paul to the Romans said:
Sin in the Scriptures means not only external works of the body but also all those movements within us which bestir themselves and move us to do the external works, namely, the depth of the heart with all its powers. Therefore the word do should refer to a person's completely falling into sin. No external work of sin happens, after all, unless a person commit himself to it completely, body and soul. In particular, the Scriptures see into the heart, to the root and main source of all sin: unbelief in the depth of the heart. Thus, even as faith alone makes just and brings the Spirit and the desire to do good external works, so it is only unbelief which sins and exalts the flesh and brings desire to do evil external works. That's what happened to Adam and Eve in Paradise (cf. Genesis 3).
That is why only unbelief is called sin by Christ, as he says in John, chapter 16, "The Spirit will punish the world because of sin, because it does not believe in me." Furthermore, before good or bad works happen, which are the good or bad fruits of the heart, there has to be present in the heart either faith or unbelief, the root, sap and chief power of all sin.
Examining the Scriptural references for
unbelief are too much to go into right away so just a quick word. Some of the Greek words translated into English as
unbelief,
believe not, and
disobedience mean "obstinate opposition", "to refuse belief", and "unwilling to be persuaded". Notice the active part of these definitions which come from our sinful nature. Other words for
unbelief simply mean "lack of".
Original Sin
Original sin as described in the various historic confessions is also a good place to look. Original sin is the sinful nature we are all born with. Several confessions are available at
Center for Reformed Theology and Apologetics website in their
Historic Church Documents section. Some examples are:
418 AD - Council of Carthage said:
This council's position on original sin was, even "new-born children... have in them... original sin inherited from Adam".
529 AD - Council of Orange said:
"... it is the whole man, that is, both body and soul, that was 'changed for the worse' through the offense of Adam's sin..."
"...also that sin, which is the death of the soul, passed through one man to the whole human race..."
1530 - Augsburg Confession said:
"...since the fall of Adam all men begotten in the natural way are born with sin, ...and that this disease, or vice of origin, is truly sin, even now condemning and bringing eternal death upon those not born again..."
It is a useful exercise to read what all of the confessions say about original sin.