After 1555, the Peace of Augsburg became the legitimating legal document governing the co-existence of the Lutheran and Catholic faiths in the German lands of the Holy Roman Empire, and it served to ameliorate many of the tensions between followers of the "Old Faith" (Catholicism) and the followers of Luther, but it had two fundamental flaws.
First, Ferdinand had rushed the article on reservatum ecclesiasticum through the debate; it had not undergone the scrutiny and discussion that attended the widespread acceptance and support of cuius regio, eius religio.
Consequently, its wording did not cover all, or even most, potential legal scenarios.
The Declaratio Ferdinandei was not debated in plenary session at all; using his authority to "act and settle," Ferdinand had added it at the last minute, responding to lobbying by princely families and knights.

While these specific failings came back to haunt the Empire in subsequent decades, perhaps the greatest weakness of the Peace of Augsburg was its failure to take into account the growing diversity of religious expression emerging in the so-called evangelical and reformed traditions.
Other confessions had acquired popular, if not legal, legitimacy in the intervening decades and by 1555, the reforms proposed by Luther were no longer the only possibilities of religious expression: Anabaptists, such as the Frisian Menno Simons (1492–1559) and his followers; the followers of John Calvin, who were particularly strong in the southwest and the northwest; and the followers of Huldrych Zwingli were excluded from considerations and protections under the Peace of Augsburg.
According to the Augsburg agreement, their religious beliefs remained heretical.
After 1555, the Peace of Augsburg became the legitimating legal document governing the co-existence of the Lutheran and Catholic faiths in the German lands of the Holy Roman Empire, and it served to ameliorate many of the tensions between followers of the "Old Faith" (Catholicism) and the followers of Luther, but it had two fundamental flaws. First, Ferdinand had rushed the article on reservatum ecclesiasticum through the debate; it had not undergone the scrutiny and discussion that attended the widespread acceptance and support of cuius regio, eius religio. Consequently, its wording did not cover all, or even most, potential legal scenarios. The Declaratio Ferdinandei was not debated in plenary session at all; using his authority to "act and settle," Ferdinand had added it at the last minute, responding to lobbying by princely families and knights.
While these specific failings came back to haunt the Empire in subsequent decades, perhaps the greatest weakness of the Peace of Augsburg was its failure to take into account the growing diversity of religious expression emerging in the so-called evangelical and reformed traditions. Other confessions had acquired popular, if not legal, legitimacy in the intervening decades and by 1555, the reforms proposed by Luther were no longer the only possibilities of religious expression: Anabaptists, such as the Frisian Menno Simons (1492–1559) and his followers; the followers of John Calvin, who were particularly strong in the southwest and the northwest; and the followers of Huldrych Zwingli were excluded from considerations and protections under the Peace of Augsburg. According to the Augsburg agreement, their religious beliefs remained heretical.
Ferdinand I, Holy Roman Emperor