Exodus 34:20

ופטר חמור AND THE FIRST OFFSPRING OF AN ASS [THOU SHALT REDEEM] — but not that of any other unclean animal (Bekhorot 5b). תפדה בשה THOU SHALT REDEEM WITH A LAMB — one gives a lamb to the priest and it remains in his possession with the character of a non-holy object (חולין — an ordinary animal). The firstborn ass is then permitted to the owner to be used for work (Bekhorot 9b). וערפתו THEN THOU SHALT BREAK ITS NECK — one breaks its neck with a hatchet and so slays it (Bekhorot 10b). The reason is: he (the owner of the ass) has caused loss to the possessions of the priest (by not giving him the lamb) therefore must he suffer loss in his possessions (Mekhilta). כל בכור בניך תפדה ALL THE FIRSTBORN OF THY SONS THOU SHALT REDEEM — Five Sela’im are the ransom fixed for him, as it is said (Numbers 18:16) “And those that are to be redeemed, from a month old shalt thou redeem [according to thy valuation, for the money of five shekels]”. (For the whole of this verse cf. Rashi on 13:13). ולא יראו פני ריקם AND NONE SHALL APEAR BEFORE ME EMPTY — According to the plain sense of the verse this is an independent statement and does not refer to the firstborn just mentioned — because in connection with the command concerning the firstborn there is no duty of appearing before the Lord; but it is another (a separate) prohibition merely connected by a conjunctive ו with the former statement and means: when you go up to the festival gathering to Jerusalem to appear before the Lord, none shall appear before Me empty; it is your duty to bring the burnt offering prescribed for the appearance before My face (Chagigah 7a). According to the Halachic explanation of the Boraitha this portion of the verse is redundant (since the same commandment already appears Exodus 23:15) and is consequently “free” (מופנה) to be used for a גז"ש (an analogy based on verbal similarity in two texts, viz., the word ריקם here and in the text Deuteronomy 15:13 לא תשלחנו ריקם “thou shalt not let him go away ריקם”) — it is repeated here after the law about the first born to teach you that the outfit given to a Hebrew slave when he leaves your service should consist of five Sela’im-worth of each of the things (mentioned Deuteronomy 15:14: thy sheep, thy threshing floor, and vinepress) just as the ransom of the firstborn is five Sela’im. Thus are we taught in Treatise Kiddushin 17a.

וּפֶ֤טֶר חֲמוֹר֙ תִּפְדֶּ֣ה בְשֶׂ֔ה וְאִם־לֹ֥א תִפְדֶּ֖ה וַעֲרַפְתּ֑וֹ כֹּ֣ל בְּכ֤וֹר בָּנֶ֙יךָ֙ תִּפְדֶּ֔ה וְלֹֽא־יֵרָא֥וּ פָנַ֖י רֵיקָֽם׃

But the firstling of an ass thou shalt redeem with a lamb: and if thou redeem it not, then shalt thou break its neck. All the firstborn of thy sons thou shalt redeem. And none shall appear before me empty.