Cassel began his career as an author with his doctor's thesis on "Die Psalmenüberschriften" (published in the "Literaturblatt des Orients," Leipzig, 1840). He received his rabbinical diploma in 1843 from Jacob Joseph Oettinger and Zecharias Frankel, but never accepted, a rabbinical position, although he possessed a decided talent for the pulpit, as may be seen from his "Sabbath-Stunden zur Belehrung und Erbauung" (Berlin, 1868), a collection of 52 homilies on the Pentateuch, originally delivered as Sabbath lectures in a school for boys.
Cassel began his writing career with his doctoral work on "The Titles of the Psalms" (published in the "Literature Review of the East," Leipzig, 1840). He received his rabbinical degree in 1843 from Jacob Joseph Oettinger and Zecharias Frankel, but never pursued a rabbinical career, despite showing great aptitude for preaching, as seen in his "Sabbath Lessons for Guidance and Upliftment" (Berlin, 1868), a compilation of 52 homilies on the Pentateuch, originally delivered as Sabbath lectures in a school for boys.