E7. Gezerah shawah (analogy): Argument from analogy. Biblical passages containing synonyms or homonyms are subject, however much they differ in other respects, to identical definitions and applications.
Rashi’s Commentary for: Shemot (Exod.) 34:20 and they shall not appear before Me empty-handed According to the simple meaning of the verse, this is a separate matter [from the rest of this verse] and is unrelated to the firstborn, because there is no obligation to appear [in the Temple] in the commandment dealing with the firstborn. Instead this is another warning, [meaning] and when you ascend [to the Temple] on the festivals, you shall not appear before Me empty-handed, [but] it is incumbent upon you to bring burnt offerings (Chag. 7a) whenever appearing before God. According to the way it is interpreted by a Baraitha, this is a superfluous verse [for this was already stated in Exod. 23:15], and it is free [i.e., has no additional reason for being here other than] to be used for a גְּזֵרָה שָׁוָה , [i.e.,] an instance of similar wording, to teach [us] about the provisions given a Hebrew slave [when he is freed]—that it is five selas from each kind [i.e., of sheep, grain, and wine], as much as the redemption of a firstborn. [This is elaborated upon] in tractate Kiddushin (17a).