At the age of 19, he edited the periodical Degel Ha'Torah, the mouthpiece of the Polish branch of Agudath Israel.

In 1924 (or 1925[1]), in response to a call from the Ger Rebbe, Rabbi Avraham Mordechai Alter, Kasher moved to Jerusalem, in Mandate Palestine, to establish the Sfas Emes Yeshiva in honour of the Rebbe's father, Yehudah Aryeh Leib Alter.

The latter part consists of the extensive annotations and addendum in which he used his awareness of variant texts as well as his almost encyclopedic knowledge in all Jewish works to clarify many obscure points in the Talmud.

Another work, Gemara Shelemah, which was to have discussed and compared variant texts of the Talmud, was never completed save for the beginning of Tractate Pesachim.

He was also the editor-in-chief for the Tzafnas Paneach Institute, publishing several volumes of Rabbi Joseph Rosen's commentary on Talmud.