Soon after the Gzerah he returned to Maribor, where he started to serve as a rabbi; already in 1425 his correspondence and socializing with other scholars of his age is attested. Such a scholar was, for instance, Anshel of Maribor (Anshel Marpurk). His authority also included ordination of other rabbis. Responsa of rabbis Israel Bruna, Moses Mintz and Jacob Moelin or the Maharil of Mainz quotes Isserlein with great respect. For an unknown reason he moved to Neustadt, where he is attested in 1445, even though due to the fact that he frequently traveled between Maribor and Neustadt, we can assume that he actually took residence in Neustadt around 1450. He dealt with money-lending only marginally and with small sums of money. In Neustadt, as before in Maribor, he started to run a yeshiva until 1460, when he died. Because of his activities he is also named R. Israel Marpurk and R. Israel of Noyshtat. On many occasions he signed himself as 'The small one and the young one in Israel' (Ha-katan ve-ha-tzair she-be-Israel).