Simplified for Easy Understanding
One who thinks that the living entity is the slayer or that he is slain, does not understand. A person who is in knowledge knows that the self slays not nor is slain.
Formal:
He who thinks that the living entity is the slayer or that he is slain, does not understand. One who is in knowledge knows that the self slays not nor is slain.
Simple:
One who thinks that the living entity is the slayer or that he is slain, does not understand. A person who is in knowledge knows that the self slays not nor is slain.