Jeremiah 31:34: Does The Lord Have Divine Amnesia?

What does the Lord mean in Jeremiah 31:34 when he says, "I will remember their sin no more"? Romans 2:6 says, "He will render to each according to his works." 1 Corinthians 3:10-15 speaks of judgment involving rewards or the loss thereof. Scripture speaks of not grieving the Holy Spirit. It seems like sin would have to be remembered in order to judge works, give rewards, or to be grieved.