Isaiah 43:25,26 - “I, even I, am the one who wipes out your transgressions for My own sake, And I will not remember your sins.  Put Me in remembrance, let us argue our case together; State your cause, that you may be proved right.”  

As long as you allow the devil to keep reminding you of past sins and failures, he will take advantage of you.  Constantly dwelling on the past will keep your faith inoperative. And as long as you have no confidence in your own faith, your prayers will be hindered. 

Why does God say that He won’t remember our sins for His own sake?  So that He can bless us!  He blots out our sins for His own sake so He can help us and demonstrate His great mercy and love on our behalf.