Hence, Ernest is known as the ancestor of the Catholic Rotenburg Quarter, a group of junior lines of the House of Hesse.

He made his Grand Tour to France and Italy, and fought with Hesse-Kassel during the final years of the war, for example at the Battle of Nördlingen on 3 August 1645.

The construction activities associated with the extension of his castle and the fact that many landgraviate authorities resided at Rheinfels, contributed significantly to the economic boom of St. Goar, which had suffered severely from the Thirty Years' War.

In 1654, a compromise was reached: the Treaty of Ravensburg allowed Ernest to create three Catholic parishes in his landgraviate, in St. Goar, Nastätten and Langen-Schwalbach.

Ernest died in 1693 and was buried, at his request, in the Pilgrimage Church in Bornhofen Monastery in Kamp-Bornhofen.