He refers to Isa. This is the business of bishops, and not of princes. God's word must contend here. If this fails, the worldly power is of no avail, though it fill the world with blood. Heresy is a spiritual thing that cannot be hewn down by iron, nor burned by fire, nor drowned by water.
Civil government is confined to external and temporal affairs.
If an emperor or prince asks me about my faith, I would give answer, not because of his command, but because of my duty to confess my faith before everybody. Luther himself changed his opinion on this subject, and was in some measure driven to a change by the disturbances and heresies which sprang up around him, and threatened disorder and anarchy. The victory over the peasants greatly increased the power of the princes. It is just the opposite of the hierarchical principle of the Roman Church, which tries to rule the state. Melanchthon justified this transfer chiefly by the neglect of the pope and bishops to do their duty.