Updated: May 31, 2021
Ask a Christian what their definition of sin is and you will get answers similar to 'rebellion against God', 'missing the mark' or 'loving something else more than God'. These are well established definitions of sin. You will find something very close to 'missing the mark' in any bible dictionary under the definition of khata, the Hebrew word translated as sin in the Old Testament, or harmatia, the Greek in the New Testament. As far as definitions go these are helpful, but for this post I wanted to dig a bit further into why missing the mark is so deserving of death that God had to defeat death to redeem humanity.
It is most commonly taught in evangelical circles and gospel presentations that sin is a crime that humanity is guilty of and from the words of Jesus, deserves an eternal punishment (see Matthew 25:41-46). Whatever eternal punishment is from this particular passage, it is the antithesis of the eternal life offered to those who Jesus calls his sheep.
In Romans 6, Paul seems to make it clear what the punishment is as he writes:
For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord.
In its context, Paul writes this verse to say that Jesus died because of the sins of the world so that the world can gain life in him. It is an echo of another famous verse found in the gospel of John:
“For God so loved the world that he gave his only Son, that whoever believes in him should not perish but have eternal life."
If we remain in sin, our end will be death but if we remain in Jesus, our end will be eternal life (see the whole of chapter 6).
So the punishment/wages/end of sin is death. Why?
Punishment is 'a penalty inflicted as retribution for an offence'. So logic suggests that sin must be a crime or offence against God. It naturally raises the question about why even a good life must deserve death if it is without God - especially if death is understood as eternal conscious torment (more on that in a moment).
Sin is more than just an immoral act. Jason Georges and Mark Baker in Ministering in Honor [sic]-Shame Cultures write (quoting Simon Chan):
Within the family context, sin is not just the wrong an individual does against some objective law. It is an affront to God's honor (Anselm) and an act that dishonors the family name...
Georges and Baker continue:
Sin is disloyalty to a relationship, not merely violating a rule. Israel's problem was that "their hearts were not loyal to him [God], they were not faithful to his covenant" (Ps 78:37 NIV), and this brought dishonour to God.
Sin came into the world through Adam and this wasn't just an immoral act. On the face of it, it was disobedience. Did eating a piece of fruit really deserve the consequence of the whole world becoming corrupt? Under the definitions given by Georges and Baker, it makes more sense to see sin as the breaking of a relationship. God gave Adam and Eve the entirety of the garden with all of the trees and their fruit except one (Genesis 2:16). Sin was to take the fruit of the knowledge of good and bad rather than trust God to give the knowledge at the right time. The Bible Project explains this as humanity 'taking the authority to do what is good in their own eyes' (echoes of Judges 17:6).
Sin is far more than just an action, though it is most easily seen through actions. Just before Cain kills Abel, God tells him:
"And if you do not do well, sin is crouching at the door. Its desire is contrary to you, but you must rule over it.” (Genesis 4:7)
Even before Cain commits murder, sin is waiting outside, a power that Cain must rule over, he fails. Justo L. Gonzales helpfully clarifies this idea of sin being outside of an individual but a state humanity is in:
"In its deepest sense "sin" is not an action, nor even an attitude, but a state, a condition in which humans find themselves estranged from God and therefore also from each other and from the rest of creation. This is part of what is meant by “original sin"—a condition into which we are all born and from which we cannot free ourselves." 
This definition makes better sense of verses such as Romans 3:23:
"for all have sinned and fall short of the glory of God"
To take this a little further, God's glory is a standard we cannot reach and so there is a disconnect between us and God because of sin. In an individualistic society, like most of the West, this idea of a broken relationship doesn't always sink in. Alan Mann in his book Atonement for a 'Sinless' Society writes,
Sin has rather unhelpfully been reduced solely to the presence of wrongful actions when in reality it would have far greater meaning for individuals... to describe it as an absence of mutual, intimate, undistorted relating that ultimately leads the self into a lack of ontological coherence.
Sin not only is an offence against God but a distortion of the self in such a way that person is not able to reach the ideal they hold for themselves. They live craving for a 'wholeness of being that always seems to be out of reach'. Mann continues to describe this idea as 'shame'.
Ephesians 2 then is a good summary of all of this. Sin cuts us off ('separated', verse 12) from the giver of life in a way that means we are like dead people walking. It is a state that is hostile to God and makes us 'objects of wrath' or in simple terms - awaiting death. A better image may be that of someone on death row, walking to their punishment with the cell mates calling out, 'dead man walking'.
Under the power of sin we cannot enter the presence of God and expect to live (a constant theme throughout the bible). We will ultimately end up dead unless we have a mediator or a substitute (or both!). The substitute was the sacrificial system in the Old Testament, an animal died so that the sinner wouldn't have to. Jesus became the ultimate sacrifice (see also Hebrews 10) so that we can live in God's presence and have the Holy Spirit in us. This sacrifice not only reconciles us with God but also with those around us, and if Alan Mann is correct, brings ontological coherence to the individual - shame is removed and we are given honour.
If sin is just an action we are guilty of, all Jesus died for was for the forgiveness of actions. Though we all need forgiveness, Easter is far more than that. Jesus died so that we no longer need live in shame but we are now 'members of the household of God' (Ephesians 2:19). Jesus died to defeat sin and the power it has over us so that God can dwell in us. Jesus died to defeat death itself so that we can have eternal life through him.
A clarification on death
Many split death into two types - physical and spiritual. The physical death is the separation of soul from body and the spiritual death as the separation from God. We all are born into a form of spiritual death and Ephesians 2 is often used to defend this. Though I would agree with the dualistic idea that physical death is the separation of the soul from the body as the body 'returns to dust', I argue that death as the punishment for sin is the opposite of living forever and the ultimate return to dust (as per Genesis 3:19-22).
What about hell?
Many define death as the ultimate separation from God and it is why they see hell as an ongoing punishment because we can be separated from God now while living physically. This, I would argue, is a confusion of death with sin. It is sin that is the separation of the self from the giver of life through a failure to love and give honour to him as already shown. Death is the result of a life lived in sin.
Ephesians 2 is often used to show a condition called spiritual death in which a person can live and walk but be called dead. I do not think this is what Paul had in mind. Given that Paul does not once use the term 'hell' in his writings, reading a cultural understanding of hell into them isn't helpful. What Paul does teach is that on the day that Jesus returns, those who do not obey the gospel of the Lord Jesus will face the flaming fire of God ('God is a consuming fire', Hebrews 12:29) and suffer eternal destruction from the presence of God (see 2 Thessalonians 1:9).
Hell, in the sense of a lake of fire, is just what John says it is in Revelation 20:14, 'This is the second death, the lake of fire'. Those who face God on their own terms, who decide what is right in their own eyes, will not be able to live in the presence of God and the lake of fire will consume them.
God, not wanting anyone to perish, has taken on death, defeated it and offers life to all through Jesus. Jesus has taken your punishment, the consequence of our rebellion, our disloyalty to God, our shame, nailed it all to the cross and said it is finished. He is the substitute, his death for your death, his life gives you life.
What about the unforgivable sin?
This is in no way an exhaustive essay about sin but a summary of my own exploration. Having recently been asked what I think about the unforgivable sin (see Mark 3:28-30) I felt I'd add my thoughts to the end of this post. This is a fairly big topic with many varying answers online but this is what I have come to think after digging into the bible.
Sin is not just one action, or even ongoing actions (we all still sin in this sense), but a state a person is in. Many are in this state out of ignorance but there are examples in the bible of people who, once they've encountered God, decide to remain in this state. This is called 'hardening their heart'. The most well known example of this is Pharaoh in Exodus 9 who sins by not letting the Israelites go despite his promises to do so. Later on in the story we see God then hardens Pharaoh's heart, giving Pharaoh over to his own sin - his own rejection of God.
The context of Mark 3 and then similar passages about sin not being forgiven (see Hebrews 10:26) show that it is a continual hardening of heart against God and a rejection of what God is doing through Jesus or the Holy Spirit (see Mark's clarification in verse 30). The bible clearly states that all who call on the name of the Lord will be saved (Psalms 86:5 and 145, Joel 2:32, Acts 2:21, Romans 10:13 and others) and God wants none to perish (Ezekiel 18 and 33 and 2 Peter 3:9 and others). If you want to live, God will receive you. If you harden your heart or continue in a state of denying that God will receive you, then you are rejecting Jesus' power to forgive and redeem you. The denial of the power of Jesus' death and the work of the Holy Spirit is a state that cannot be forgiven. If it were to be forgiven it would go against your will to reject God's grace.
God's grace is freely given so that we can freely receive. You also have an option to freely reject it and face the consequence of your sin. You can pay your own wage but you are unlikely to remain alive if you do.
A final word
The good news of Jesus is that sin is defeated. We don't have to live in it any longer. We can know God and begin to live in the eternal life that he offers now. We look forward to a new creation where death will be no more. Easter is the hope that death is just a doorway to life as it was meant to be. If you have read this essay and do not know Jesus, I would love for you to get in touch and talk about this some more.
Resources and quotes:
If sin deserves an eternal conscious torment, it is a significant omission by Paul when talking so clearly about what Jesus' death achieves. For further interaction with Paul's writing and the biblical context against this argument, see an article by Joseph Dear at Rethinking Hell or read my own essay exploring the punishment of sin and God's judgement.
Ministering in Honor-Shame Cultures, Jayson Georges and Mark D. Baker
See also Malachi 1:6 and 2:2-3, Psalms 106:20, Jeremiah 2:11 and Romans 1:21-23 for further biblical backing.
Justo L. Gonzalez, Essential Theological Terms, with thanks to Ian Davies in UK Apologetics and Evangelism Group on Facebook.
Atonement for a 'Sinless' Society, Alan Mann
Many translations say the eternal destruction is 'away' from the presence of God but there is no reason to add this in the original Greek. 'Apo' simply means from and is used and translated correctly in the second 'from' in the very same verse.
The lake of fire is a vision of God's presence based on Isaiah and Hebrews who both call God the 'consuming fire' and Isaiah says only the righteous can live with 'everlasting burnings', Isaiah 33:14-15. This will be looked at in more depth on this blog as I go through Revelation over the next few weeks. See also my own essay in point 1.