In I John 3:4b we see a short answer to this question, in fact that verse defines exactly what sin is.  When we look at that verse defining sin and then look at the scope of sin we see how menacing a thing it is.  I John 3:4b reads, “for sin is the transgression of the law.”  To understand sin we must define transgression.  To transgress is to go beyond something (you might even compare it to trespassing, i.e. going beyond boundaries that another has set).  To say that sin is a transgression of the law is to say that we sin when our actions, or thoughts, go beyond what is allowed by God’s law.  To illustrate this definition, picture a path winding its way along the side of a sheer cliff, a deadly drop off awaiting any who should step off the path.  That path would be the law of God, the cliff would be sin.  To go beyond the boundaries of the path would mean sure death.
Notice that in that particular illustration the result is death.  This is how God described the scope of sin:  Death.  While the former would be a physical death, the latter is a spiritual death (death being a separation) separating man from God.  Romans 6:23 reads, “For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.”  The scope of sin in this sense is alienation from God, and that is why it was necessary for one who knew no sin to give His life that those who have sinned might be given an avenue by which they could return to the path.
    Finally notice the scope of sin in another way.  I suppose that there are some who  think that they are above sin.  I John 1:8 teaches of such an attitude, “If we say that we have no sin, we deceive ourselves, and the truth is not in us.”  Romans 3:23 teaches “For all have sinned, and come short of the glory of God.”  Now notice what we have learned about sin:  Sin, at some point committed by all, is the breaking of God’s law, the result of which is separation from He and His blessings.
    If all have sinned, and that sin leads to an eternal separation, then where is the hope for man?  The whole of the Bible teaches that the hope is in Christ (John 3:16).  In closing notice Romans 6:3-6 to see how man can overcome sin and therefore be reconciled to God. “Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death?  Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.  For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection:  Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.”