If we are to serve God we must act as servants of the True King, Jesus Christ, Son of God. He will never forget all we do for Him. Conversely, He will never forget our wrongdoing.
Scoundrels know how the world works and they can do their evil on the good and virtuous.
Servants of the Lord must know the ways of the Kingdom of Heaven if they mean to arrive there. We must not take salvation for granted, but ask for the grace and mercy of God. God will never forget the doings of the wicked. God is justice. Neither will God forget the mercy of the good.