Adam Clarke on John 15:21

Because they know not him that sent me - This is the foundation of all religious persecution: those who are guilty of it, whether in Church or state, know nothing about God. If God tolerates a worship which professes to have him for its object, and which does not disturb the quiet or peace of society, no man has the smallest right to meddle with it; and he that does fights against God. His letting it pass is at least a tacit command that all should treat it as he has done.