Besides some secular compositions, as the genre pictures of the life of the common people at Rome, he treated pre-eminently scenes and persons of the Old and New Testaments.

His pictures of the Adoration of the Shepherds, Christ as the Friend of Children, Awakening of the Young Man of Naim, Tribute Money, Jacob and Esau, and The Finding of Moses, are in the spirit of Overbeck.

The St. Anthony, and St. Benedict, as engraved by the Capuchin Bernardo da Monaco, and his Mater Amabilis aroused admiration; an enthroned Madonna went to England.

In the Trinità dei Monti in Rome he painted in fresco the return of the Prodigal son and Christ with heart aflame.

[citation needed] Seitz was one of many who commissioned to paint frescoes for the Metropolitan Cathedral of Athens of the Annunciation (Orthodox Church of Greece).