Romans 5:15
But the gift is not like the trespass. For if the many died by the trespass of the one man (Adam), how much more did God's grace and the gift that came by the grace of the one man, Jesus Christ, overflow to the many!
Matthew 9:13
But go and learn what this means: 'I desire mercy, not sacrifice.' For I have not come to call the righteous, but sinners.
Matthew 12:7
If you had known what these words mean, 'I desire mercy, not sacrifice,' you would not have condemned the innocent.
We are all sinners. The Bible explains how and why, but you don't even need the Bible to figure out that you don't always do the right thing, not even when you seriously want to. You know your country has laws which you don't always obey. The most amazing thing that Christ teaches is that with the realisation that you are guilty, a sinner, comes the realisation that Jesus took the punishment in your place.
John 3:16
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.
It is not belief in God that saves you, therefore even doubt is no excuse. It is accepting that Jesus died and arose again. Our condemnation does not come from God, but from the rejection of the law by which we are saved (Rom.8). Think about it hypothetically: Legally, if a law is passed and you do not obey it, it is by the law that you are guilty and not by the authority that passed it.
Romans 8
33Who will bring any charge against those whom God has chosen? It is God who justifies. 34Who is he that condemns? Christ Jesus, who died--more than that, who was raised to life--is at the right hand of God and is also interceding for us. 35Who shall separate us from the love of Christ? Shall trouble or hardship or persecution or famine or nakedness or danger or sword?
Jesus came to fulfill the laws passed by God, under which we are all guilty. By admitting guilt of sin (repentance), you voluntarily submit to the law under which sin is defined - God's law. And Jesus gave us the Holy Spirit to be our councillor. If you deny the authority of the law, you also deny the authority by which you are justified.
Rom.8:22We know that the whole creation has been groaning as in the pains of childbirth right up to the present time. 23Not only so, but we ourselves, who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for our adoption as sons, the redemption of our bodies. 24For in this hope we were saved. But hope that is seen is no hope at all. Who hopes for what he already has? 25But if we hope for what we do not yet have, we wait for it patiently.
26In the same way, the Spirit helps us in our weakness. We do not know what we ought to pray for, but the Spirit himself intercedes for us with groans that words cannot express.
My point is: what is more powerful: justice, or mercy? The gospel is one of mercy - by repentance and forgiveness. You don't have to be a Christian to accept that.