Martin Luther in his Commentary on Galatians tells us how to answer the Accuser:

Paul does not say that works are objectionable, but to build one’s hopes for righteousness on works is disastrous, for that makes Christ good for nothing.  Let us bear this in mind when the devil accuses our conscience.  When that dragon accuses us of having done no good at all, say to him,”You trouble me with the remembrance of my past sins;  you remind me that I have done no good.  But this does not bother me, because if I were to trust in my own good deeds, or despair because I have done no good deeds, Christ would profit me neither way.  I am not going to make Him unprofitable to me.  This I would do if I should presume to purchase for myself the favor of God by my good deeds or if I should despair of my salvation because of my sins.”

This reminds me of my favorite hymn line:

Well may the accuser roar, of sins that I have done;

I know them all and thousands more, Jehovah knoweth none!