A DEFINATION OF SIN:
Excerpted from a talk given by Shaikh Hamza Yusuf
The literal meaning of sin is “missing the mark” Thus when one is trying to be righteous (which is the bull’s-eye) but one misses the bull’s-eye, that is sin.
Allah’s Messenger (sal Allahu alaihi wa sallam) said: “Beware of sins which are treated as being minor, just like a people who encamp in the centre of a valley, so someone brings a stick of firewood and someone else brings a stick until they are, therefore, able to bake their bread. (I.e. many small sticks collected became important or significant enough that a fire could be lit) Likewise, sins which are treated as being minor, and for which the person is taken to account, will destroy him.” [Ahmad]
It is just as the noble companion Abdullah ibn Masood (radi Allahu anhu) said: “The believer sees his sins as if he were sitting beneath a mountain which he feared was about to fall upon him, whereas the wicked sees his sins like a man who finds a fly settle upon his nose, so he does this (the narrator brushed it away from his nose).”
The Muslim should realize the greatness of his Lord, the One free and far from all imperfections, and His tremendous Power and Might, and he should not think of the sin as being great or small! Rather he should think of it with regard to the One whom he is disobeying.
The committing of sin removes eemaan and fear of Allah (subhana wa ta’ala) from the heart. Each sin leaves a black dot upon the heart, killing it a little bit. When the heart is covered in black, a seal is then put on it and the door of guidance is shut on it. The sins, which are ignored, neither repented for nor erased by the doing of good deeds, cause their doer’s destruction.