Why is sin a misconception of reality?

Remember; all sin is but a mistake―a misconception of reality―hence, it needs not only forgiveness, but, also, correcting, redeeming, and wiping out. 

And for this, you need to understand it. 

Once you understand how to develop your faculties to attain godliness, and seek for the Inner Light, and permit it to shine through the physical, then there will be no sin to forgive, for you will have followed His guidance and become like unto Him.