When the Torah describes the ear-boring of a Hebrew bondsman who chooses to remain in service, it says "his ear" shall be pierced. But which ear — left or right? The Mekhilta determines this through a technique called gezeirah shavah, a verbal analogy between two passages.
The word "his ear" appears here, and the same word appears in (Leviticus 14:25) in connection with the purification of a poor leper. In that passage, the right ear is explicitly specified. Since the same phrase is used in both contexts, the rabbis concluded: just as the leper's right ear is meant, so too the bondsman's right ear is pierced.
This method of legal derivation — linking two verses through a shared word or phrase — was one of the fundamental tools of rabbinic interpretation. The Torah does not always spell out every detail. When it leaves a gap in one passage, the rabbis looked for the same language in another passage where the detail is provided. The shared vocabulary created a legal bridge between the two texts.
The specificity matters practically. A bondsman pierced in the wrong ear has not fulfilled the Torah's requirement. The ceremony is precise: it is the right ear, at the doorpost, with an awl. Every element has a source, and the Mekhilta traces each one to its textual origin. Nothing in the ritual is left to custom or convenience. Even the choice of ear is determined by cross-referencing Scripture with Scripture.