“If anyone, then, knows the good they ought to do and doesn’t do it, it is sin for them.”
Many say that ignorance is bliss. The notion here is that if I have knowledge of my actions then that is what causes my worry and distress. Which is true, it is the knowing that makes us guilty even before we commit the act. BUT ignorance is false justification; it can’t make us happy, only our trust in God can do that. A more fitting phrase would then be: Do right, be righteous! That’s bliss.