The next element of definition in titulus I of Justinian’s Institutes is iuris prudentia.
Iuris prudentia est divinarum atque humanarum rerum notitia, justi atque iniusti scientia.
“Discretion in the application of justice [or good sense in the discernment of what is just] is an awareness of [acquaintance with/knowledge of] divine and human matters, the knowledge of [skill in/expertise in] the just and the unjust.”
The phrase iuris prudentia (for it is two words, not one) is normally just transliterated as “jurisprudence” rather than translated. I have done the opposite in order to get at what the phrase itself actually means. Prudentia is a kind of good sense, practical judgment, or skill in or acquaintance with a thing; that “thing” here is ius, what is right or just. “Jurisprudence,” then, is good sense or judgment about what is right.
Of iuris prudentia there are predicated two things, notitia and scientia, both of which are modified by a doublet in the genitive and both of which can be translated as “knowledge,” but between which there is perhaps some distinction.
First: notitia, whence the English word “notice,” derives from the verb nosco, “to become acquainted with, come to know” (in the perfect, “to have become acquainted with, know”). So: knowledge through acquaintance or practice. This is a knowledge of “things” (rerum), things, specifically, of two kinds: divinarum atque humanarum, things divine and human. Jurisprudence, then, is an acquainted-knowledge, a practiced and practical knowledge, of matters that pertain not only to human affairs, but also of those that pertain to divine affairs.
Next: scientia, whence the English word “science,” derives from the verb scio, “to know, understand, have skill in, have expertise in.” Scientia too, that is, is a knowledge that comes from practice and experience, and in that respect is similar to notitia. But he possession of scientia can also imply the further nuance of the possession of expertise, and so the word here may gesture toward systematic or comprehensive knowledge, and in that respect may be more expansive than notitia. 1
The doublet modifying scientia is of a different kind from the previous one: divinarum atque humanarum had to do with two different planes of experience together comprehensive of our world, while iusti atque iniusti has to do with opposites, though this pair too is comprehensive after a different fashion (and again there is an etymological link to ius). We might say that the first looks at our world from the cosmic or synthetic viewpoint and the second from the moral viewpoint. He who would practice justice must have an acquaintance with both human and divine things and skill in discerning what is ius and what is not ius in each.
What is most surprising to the modern reader, I would guess, is the contention that jurisprudence involves divine matters, which we suppose to belong elsewhere, outside of the realm of the jurist; but the claim was not surprising in antiquity, nor would it have been surprising until fairly recently in human history. As Thomas Collett Sandars points out in his edition of the Institutes:
Jurisprudentia is the knowledge of what is jus, and jus, according to the theory of the law of nature, laid down what is commanded by right reason, this right reason being common to the divine scheme of things and to man. On this ground, and also because public law has to deal with religious worship, the knowledge of divine things was necessary, as well as the knowledge of human things, to say what were the contents of jus.
That kind of idea about religion has a long afterlife–hence Thomas classes religion with the cardinal virtues (prudence, justice, temperance, fortitude) under the heading of justice rather than with the theological virtues (faith, hope, and charity).