But as he could not enter the Bavarian state administration because he was a Jew, he left the university and returned to his home region in 1840.
[3] In 1854, Felsenthal immigrated to America and settled in Madison, Indiana, where he worked as a rabbi and teacher for three years.
He focused on rabbinical and theological study while working as a clerk with Greenebaum Brothers, and he was ordained a rabbi by David Einhorn and Samuel Adler.
He was one of the first Jews born in Western Europe to favor participation in the First Zionist Congress in Basel, Switzerland in 1897.
He wrote an elementary grammar on the Hebrew language in 1868, several pamphlets, and 250 miscellaneous essays for periodicals.
[6] Felsenthal was opposed to Isaac Mayer Wise and the establishment of a rabbinical seminary, as he did not believe American Jewry was ready for it, and in 1878 he declined an offer to teach at Hebrew Union College.
He participated in the Philadelphia Rabbinical Conference in 1869, but he was generally opposed to establishing an American Synod.
While he generally was not politically active, in 1882 he declared himself a candidate in the Illinois Senate, writing in the Chicago Tribune that he was opposed to Sunday laws, prohibition, and blind party loyalty in local affairs.