In order to free his mother’s soul from purgatory he is ordered to kill those that have sinned against God.
These people deserve to die. They have yet to seek redemption for their evil ways.
With each kill he waits to see if his mother’s soul is finally set free. Only then can the killing stop.
The Seven Deadly Sins–Pride, Envy, Lust, Sloth, Anger, Gluttony, and Greed
“Sin creates [an inclination] to sin; it engenders vice by repetition of the same acts. This results in perverse inclinations which cloud conscience and corrupt the concrete judgment of good and evil. Thus sin tends to reproduce itself and reinforce itself, but it cannot destroy the moral sense at its root.”
Para. 1865, Catechism of the Catholic Church, 1994