John Allen's discussion of Judaism dates to 1816; for many years, it was the authoritative history of the Jews from the time of Abraham through to the modern day.

When sourcing the information necessary for this account, the author was discerning and meticulous: the history of the Jews is a topic of enormous depth and scope, requiring the use of holy books and written records often centuries or millennia old. Principally he examines the Holy Bible, and in particular the pertinent Old Testament texts, plus the holy books of the Jews such as the Kabbalah and Talmud. Other more esoteric sources include the Spanish and Portuguese Jews' Prayer Book. Each chapter of Modern Judaism includes numerous notes, elaborating further and list the relevant passages.

Many wide-ranging aspects of Jewish life are covered; such as how to manage births, marriages, deaths, the preparation of food and the care of pregnant women. The ancient temple and its precepts are extensively narrated, that readers comprehend how the Jewish faith changed and evolved as the centuries passed, with rabbis across the ages contributing to the written lore. This reprint reproduces the tables and Hebrew script of the expanded second edition, which was first published in 1830.