Exodus 13:12

והעברת This word והעברת is an expression for “setting apart”. Similarly it says, (Numbers 27:8) “And ye shall set his inheritance apart (והעברתם) for his daughter” (Mekhilta). שגר בהמה DROPPED BY BEAST— a premature birth; and this is termed שגר because its mother casts it out (שגר) and expels it (שלחתו) from the womb before its due time (שגר is a synonym of שלח “to let go”). Scripture teaches you that although it is a premature birth it is nevertheless holy by reason of its being first born, in so far that it exempts from the law regarding the firstborn the young that comes (is born) after it (Mekhilta). It is true that an animal that is not a premature birth) is also called שגר, as (Deuteronomy 7:13) “the שגר of thy kine” (where it speaks of blessing this, and it is therefore evident that it cannot there denote a premature birth), but this שגר (i. e. its use here) is intended only to tell us something about a premature birth, because, you see, it has already written in this verse: “Every first offspring of the womb”! And if you say that also the firstborn of an unclean animal (and not a premature birth) is implied by שגר (and that this also must be hallowed) then I reply that Scripture comes and expressly states in another passage, (Deuteronomy 15:19) “[All the firstling males that are born] of thy herd and of thy flocks (thus only clean animals) [shalt thou sanctify etc.]”. Another meaning may be given in explanation of והעברת כל פטר רחם “thou shalt set apart every first born of the womb” — viz., that Scripture by the term פטר רחם is speaking of the firstborn of man (consequently the following words, שגר בהמה, need not denote an animal of premature birth, but an animal born in the natural course as it certainly means in Deuteronomy 7:13, and we thus avoid the necessity of here assigning to שגר a meaning different from that which it bears in the latter passage).

וְהַעֲבַרְתָּ֥ כׇל־פֶּֽטֶר־רֶ֖חֶם לַֽיהֹוָ֑ה וְכׇל־פֶּ֣טֶר ׀ שֶׁ֣גֶר בְּהֵמָ֗ה אֲשֶׁ֨ר יִהְיֶ֥ה לְךָ֛ הַזְּכָרִ֖ים לַיהֹוָֽה׃

that thou shalt set apart to the Lord all that opens the womb, and every firstling that comes of a beast which thou hast; the males shall be the Lord’s.