It is chiefly in hermeneutics that Ernesti has any claim to eminence as a theologian.
The grammatical work of Rabbi Jonah extended, moreover, to the domain of rhetoric and biblical hermeneutics, and his lexicon contains many exegetical excursuses.
Among his principal works are: - Sacred Hermeneutics Developed and Applied (1843), rewritten and republished as A 'Treatise on Biblical Criticism (1852), Lectures on Ecclesiastical Polity (1848), An Introduction to the New Testament (1848-1851), The Hebrew Text of the Old Testament Revised (1855), Introduction to the Old Testament (1862), On a Fresh Revision of the Old Testament (1873), The Canon of the Bible (1877), TheDoctrine of Last Things in the New Testament (1883), besides translations of the New Testament from Von Tischendorf's text, Gieseler's Ecclesiastical History (1846) and Fiirst's Hebrew and Chaldee Lexicon.
Yet his first courses of lectures in that department were readings and expositions of the Old and New Testament; and to this, as also to hermeneutics, he always attached special importance, believing that for theology a sound exegesis was the one indispensable requisite.
In 1843 Eadie was appointed professor of biblical literature and hermeneutics in the Divinity Hall of the United Presbyterian body.
He laid down seven rules for the interpretation of the Scriptures, and these became the foundation of rabbinical hermeneutics; and the ordering of the traditional doctrines into a whole, effected in the Mishna by his successor Judah I., two hundred years after Hillel's death, was probably likewise due to his instigation.
In 1784 he was appointed professor of Oriental languages and hermeneutics in the university of Lemberg, when he took the degree of doctor of divinity; and shortly afterwards he was released from his monastic vows on the intervention of the emperor.