Sin
What sin is and why it's bad news
What is sin?
Sin is the reason we need a saviour. Sin is what separates us from God.
We see from the bible that sin at its core is disobedience and rebellion against God.
The first sin that humanity committed was an act of disobedience toward the command that God had given them and an act of rebellion in their hearts against God, choosing to be their own god rather than submitting to the Lord God (You can read more about humanity's first sin under The Original Sin). This account also shows us the consequence and severity of sin which is expanded on under the section "Sin brings death".
We then see throughout the Old Testament how the Israelites would sin and disobey God over and over again. And for this God calls them rebellious:
We also see from 1 John 3:4 that sin is lawlessness. If we look at Strong's G459; "ἀνομία", we see that the Greek word for lawlessness means to transgress or violate the law of God, also being defined as unrighteousness and wickedness.
Another perspective is Strong's H2398; "חָטָא", which defines sin as missing the way or missing the mark (for example an archer whose arrow falls short of hitting the target). This view of sin describes well how God's standard is holiness (1 Peter 1:16) and perfection (Matthew 5:48), and anything short of that is not good enough. And we see this reality in James 2:10:
This is an extremely high standard to fulfill the requirement of righteousness, and you'll see later why no human is capable of this in and of themselves.
In summary; sin is an act of disobedience or a heart of rebellion against God and/or His law.
Sin brings death
The consequence of sin is exceedingly severe; that is, death:
But this death that the bible is talking about is a spiritual death. When Adam and Eve sinned, they didn't physically die until hundreds of years later even though God said that the day they eat from the tree of the knowledge of good and evil they will die (Genisis 2:17). We can also see this concept of spiritual death in Ephesians 2:1, Ephesians 4:18, and Colossians 2:13.
Now being spiritually dead really means to be separated from God, alienated, cut off, having no relationship with God, not knowing Him. Or "being alienated from the life of God" as Ephesians 4:18 says.
You can think of this spritual death like a branch that has been cut off from the tree. Even though the branch might still physically appear alive at first, its connection to the source of life has been severed and it is sure to die. It's already spiritually dead. It no longer recieves water or nutrition from the branch.
Likewise with us, if we are spiritually dead we have been cut off from the source of life which is God, and we no longer have any capacity for relationship with Him. We are totally lost without Him. In this state we don't know God and as a result it's impossible for us to truly love others. The love we think we had was actually human emotion and selfish need and desire.
Moreover, this spiritual death is an eternal death. Eternal separation from God. In this state, we can't go to heaven and be with the Lord face to face forever. God is first and foremost love, but He is also a just and righteous judge, who takes sin very seriously and will punish sin. If anyone is found to be unrighteous on the day of judgement, He will throw them into Hell because the wages of sin is death; or in other words, the fruit that you reap from sowing the seed of sin is death.
All have sinned
Most people think that they are a good person. They don't think they've done anything so substantially wrong to warrent going to Hell. But the reality is that we've all sinned:
Where does sin come from?
The devil and the flesh
The deceptive nature of sin
Sin decieves. People supress the truth in unrighteousness.