His father, Israel ben Josef (known as Isserl), was a prominent talmudist and independently wealthy,[3] who had probably headed the community; his grandfather, Jehiel Luria, was the first rabbi of Brisk.

Among his fellow pupils were his relative Solomon Luria (Maharshal)—later a major disputant of many of Isserles' halachic rulings,[5] and Chayyim b. Bezalel, an older brother of the Maharal.

His first wife died young, at the age of 20 and he later established the "Rema Synagogue" in Kraków in her memory (originally his house, built by his father in his honor—which he gave to the community).

At this point, the Responsa of still later authorities are cited extensively in accordance with the well-established principle of הלכה כבתרא, paying due attention even to the opinions of contemporaries and to customs of Polish Jewry which the ב”י omitted.

Thus, Isserles, in his responsa as well as in the ד”מ and his commentary on the Shulchan Aruch, served as a supplement and offered his community the code of Law adjusted to its authorities, customs, and needs.

"[15] Isserles, like Yosef Karo in the Shulchan Aruch, often quotes Kabbalistic sources and opinions in his various works, and writes of his great joy upon finding that his ruling concurred with what he later found written in the "words of the Zohar which were given at Sinai...".

[16][17] Isserles is renowned for his fundamental work of Halakha (Jewish law), entitled ha-Mapah (lit., "the tablecloth"), an inline commentary on the Shulchan Aruch (lit.

Recognizing that Karo's commentary largely met his objectives, Isserles published the Darkhei Moshe in a modified form.

"In publishing the דרכי משה, R. Isserles rendered a great service to Ashkenazic Jewry, for he reestablished its Talmudic authorities as the deciding factor in determining a law.

HaMapah (המפה) is written as a gloss to the Shulchan Aruch of Yosef Karo, discussing cases where Sephardi and Ashkenazi customs differ.

Karo had based his normative positions on three authorities: Maimonides, Asher ben Jehiel (the Rosh), and Isaac Alfasi (the Rif).

Of these, only Asher ben Jehiel had non-Sephardic roots, having lived most of his life in Germany before moving to Spain, but even so, his work is largely Sephardic in orientation.

All editions of the Shulchan Aruch since 1578 include HaMapah embedded in the text (introduced by the word: הגה Hagahah, meaning "gloss"), and distinguished by a semi-cursive "Rashi script".

Isserles' HaMapah was "considered to be an interpretation and supplement to Karo's work, while also challenging its claim to universal authority by introducing Ashkenazic traditions and customs that differed from the Sephardic ones.

It is through this unification that the Shulkhan Aruch became the universally accepted Code of Law for the entire Jewish people, with the notable exception of Yemenite Jews who still follow the Rambam (Maimonides).

In addition to discussing the principles of the Jewish faith invoked, Isserles connects the Torah laws and symbols to philosophy, physics, astronomy, and Kabbalah.