Financial aid was given to the Huguenots, and Hessian troops fought side by side with them in the French religious civil wars, this policy contributing to the declaration of toleration at Amboise in March 1563. He gave permanent form to the Hessian Church by the great agenda of 1566–67, and in his will, dated 1562, urged his sons to maintain the Augsburg Confession and the Concord of Wittenberg, and at the same time to work in behalf of a reunion of Roman Catholics and Protestants if opportunity and circumstances should permit.