Sin - The committing of any act that God has forbidden, or the neglect of any act that God has commanded.
All are sinners.
I came to the realization that my theology is driven by my understanding of sin. My understanding of salvation is based on my understanding of sin. Salvation is by substitutionary atonement because our sin has rendered us guilty and helpless. My understanding of the sovereignty of God in salvation is driven by the fact that our sin has not only left us guilty but dead, unable to save ourselves or respond to God's gracious offers without His supernatural work.
My understanding of who Christ is is driven by my understanding of sin. Jesus came to die for sinners because we are guilty and helpless, we must have a savior, a mediator between we the sinners and God the Holy One. Without understanding sin the Incarnation of Jesus makes no sense, why bother becoming man if there is no grand mission to save sinners. The Cross of Christ makes no sense apart from the Biblical understanding of sin, because what on earth is Jesus doing on the cross if He is not dying for sin, it is simply tragic.
If we give in to our culture that denies the reality of sin, we have not made Christianity more palatable to the world. Rather we have given away the whole store. Without the right understanding and acknowledgment of sin we no longer have an orthodox view of God, and the Gospel descends into simple nonsense. Without the correct understanding of sin, we are still in our sins and will face death and hell as the just judgment for our sin.
So we need to embrace the Biblical view of sin, and let it sink deeply into our minds and hearts. Then we begin pursuing holiness and we carry the Gospel to our sin-sick world.