Falling short of God's glory - His standard or mark of righteousness and holiness.

Sin is lawlessness (1 John 3:4) or transgression of God's will, either by omitting to do what God's law requires or by doing what it forbids.

The transgression can occur in thought (1 John 3:15), word (Matt 5:22), or deed (Rom 1:32).

Mankind was created without sin, morally upright and inclined to do good (Eccl 7:29).

But sin entered into mankind when Adam and Eve disobeyed God by eating the forbidden fruit in the Garden of Eden (Gen 3:6).

Being the head of the whole human race, Adam's sin affected all future generations (Rom 5:12-21). His fallen nature was passed on to all his descendants. Out of this, man committed all kinds of sins (Matt 15:19); and no one is free from sin (Rom 3:23).

by: Joshua Ong

Sources:

• Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary
• Nelson's Illustrated Bible Dictionary