To identify himself more completely with his followers, the prince, October, 1573, openly announced his adhesion to Calvinism.

There are no grounds for doubting his sincerity in taking this step; it was not an act of pure opportunism.

His early Catholicism had probably been little more than an outward profession, and as soon as he began to think seriously about religious questions, his natural bent had led him first to the Lutheran faith of his family, and then to the sterner doctrines, which had gained so firm a foothold in the towns of Holland and Zeeland.

Nevertheless William, though henceforth a consistent Calvinist, was remarkable among his contemporaries for the principles of religious toleration he both inculcated and practised.

He was constitutionally averse to religious persecution in any form, and by the zealots of his party he was denounced as lukewarm; but throughout his life he upheld the right of the individual, who was peaceful and law-abiding, to liberty of opinion and freedom of worship.
The year 1574 opened favourably.