Exegesis is essentially interpretation of a text, though typically it refers to interpreting difficult or challenging texts.
In the case of text-based religions (particularly Islam, Judaism, and Christianity) exegesis refers to the rule-based process of determining the original meanings of their sacred texts. The difficulties related to such exegesis are due to the differences between older understandings and current expectations.
Thus both ancient texts (such as the Hebrew Bible / Christian Old Testament) and antiquarian texts (such as the Christian New Testament) were written using conventions and according to standards that are very different from those used in today’s letters or novels. The result is that modern readers easily overlook these conventions or misinterpret these standards, and so misunderstand the text’s original meaning.
Now “original meaning” is crucial. For example, Christians and other religious adherents claim to live their lives in accordance with certain standards—to act and think in certain ways, to certain ends. Yet how do we know what those standards are? Christians rely on sound exegesis in order to apply the Bible’s meaning within its original context to the new and different contexts in which they find themselves.
So the text’s current meaning, or application, must be informed by / related to its original meaning(s).
For this reason also exegesis is “rule-based.” In other words, because ancient and antiquarian texts consistently present certain differences from modern texts, exegetes (people performing exegesis) seek to treat all such texts fairly by treating them similarly.
The core of this uniform treatment originates with the hermeneutical principle of “context.” Hermeneutics is the theory and practice of interpretation and, as such, exegesis is a subset—or form of—hermeneutics.
“Context” comes into play within exegesis in various ways.
For example, properly exegeting the Bible requires reading its various books in context—reading them as ancient / antiquarian texts written according to various literary forms (narrative, prophecy, wisdom literature, etc.). It also means reading these texts as documents containing various literary devices (hyperbole, parable, chiasm), composed for a particular audience, to certain ends (to inform, persuade, denounce, etc.).
The text’s historical context is also essential as some familiar notions had quite different meanings in earlier times, as well as having different meanings between ancient and antiquarian time periods, or between Judean and Greco-Roman cultures (the notion of slavery is a prime example). Readers further need to be aware of the context for authorship and authentication, in that there were different rules for claiming authorship of a text, different standards for what counts as “historical,” and different rules for how stories could blend factual information and literary embellishment.
In terms of linguistic context, the Bible was not written in English and so readers need to understand—or at least be aware of—the nuances of the original languages. Further, as the Bible was a composite texts (that is, the Bible was pieced together by scholars from various ancient scrolls and fragments of texts) readers need to be aware of some of the issues related to this task of re-composition, knows as “text criticism” (which simply means critically assembling a large text from smaller pieces).
Now for a few caveats.
First, exegesis does not imply finding the “one true meaning” to a text, but rather the text’s domain of meaning in light its full, historical context. So this may mean that there are 4 valid meanings to a passage, of which one or two seem best for various reasons. Second, exegesis does not imply that reason alone is the sole or best method of understanding a text like the Christian Bible. Indeed, the interplay between experience and text is crucial, because the two are meant to mutually informing. Yet to be clear, we are never “simply experiencing” something (such as experiencing love or cold or a vacation) but we are always interpreting our experiences.
This means that while reason cannot “go it alone,” neither can Christians dispense with reason–and with developing a skilled use of reason–when trying to exegete the Bible.