Pre-Shabbat Message for Parashat Tzav 5780
(טז) וְאִם־נֶ֣דֶר ׀ א֣וֹ נְדָבָ֗ה זֶ֚בַח קָרְבָּנ֔וֹ בְּי֛וֹם הַקְרִיב֥וֹ אֶת־זִבְח֖וֹ יֵאָכֵ֑ל וּמִֽמָּחֳרָ֔ת וְהַנּוֹתָ֥ר מִמֶּ֖נּוּ יֵאָכֵֽל׃ (יז) וְהַנּוֹתָ֖ר מִבְּשַׂ֣ר הַזָּ֑בַח בַּיּוֹם֙ הַשְּׁלִישִׁ֔י בָּאֵ֖שׁ יִשָּׂרֵֽף׃ (יח) וְאִ֣ם הֵאָכֹ֣ל יֵ֠אָכֵל מִבְּשַׂר־זֶ֨בַח שְׁלָמָ֜יו בַּיּ֣וֹם הַשְּׁלִישִׁי֮ לֹ֣א יֵרָצֶה֒ הַמַּקְרִ֣יב אֹת֗וֹ לֹ֧א יֵחָשֵׁ֛ב ל֖וֹ פִּגּ֣וּל יִהְיֶ֑ה וְהַנֶּ֛פֶשׁ הָאֹכֶ֥לֶת מִמֶּ֖נּוּ עֲוֺנָ֥הּ תִּשָּֽׂא׃
(16) If, however, the sacrifice he offers is a votive or a freewill offering, it shall be eaten on the day that he offers his sacrifice, and what is left of it shall be eaten on the morrow. (17) What is then left of the flesh of the sacrifice shall be consumed in fire on the third day. (18) If any of the flesh of his sacrifice of well-being is eaten on the third day, it shall not be acceptable; it shall not count for him who offered it. It is an offensive thing, and the person who eats of it shall bear his guilt.
ואם האכל יאכל - חכמים עקרוהו מפשוטו. ופירשוהו במחשב לאכול מזבחו ביום השלישי באחד מד' עבודות: שחישב בשחיטה, או בהולכת הדם, או בקבלה, או בזריקה.
ואם האכול יאכל, our sages ignored the plain meaning of this verse, interpreting it as referring to the owner planning to eat of the sacrificial meat on the third day [not provided for in the Torah. Ed.] or planning not to perform any of the 4 basic procedures during the time frame designated by the Torah. (Zevachim 29)
ואם האכל יאכל וגו'. בִּמְחַשֵּׁב בַּשְּׁחִיטָה לְאָכְלוֹ בַּשְּׁלִישִׁי הַכָּתוּב מְדַבֵּר; יָכוֹל אִם אָכַל מִמֶּנּוּ בַּשְּׁלִישִׁי יִפָּסֵל לְמַפְרֵעַ, תַּלְמוּד לוֹמַר הַמַּקְרִיב אֹתוֹ לֹא יֵחָשֵׁב — בִּשְׁעַת הַקְרָבָה הוּא נִפְסָל וְאֵינוֹ נִפְסָל בַּשְּׁלִישִׁי; וְכֵן פֵּרוּשׁוֹ: בִּשְׁעַת הַקְרָבָתוֹ לֹא תַּעֲלֶה זֹאת בְּמַחֲשָׁבָה, וְאִם חִשֵּׁב פִּגּוּל יִהְיֶה (זבחים כ"ט):
אם האכל יאכל וגו' ‏ AND IF ANY [OF THE FLESH] SHOULD BE EATEN AT ALL [ON THE THIRD DAY) — Scripture is speaking of one who has the intention whilst slaughtering thė sacrifice to eat it (the flesh) on the third day. One might think that what the text really means is, that if one has eaten of it on the third day it becomes disqualified retrospectively (i. e., that it is regarded as having been invalid from the moment that it was offered)! Scripture, however, states, “As for him that offereth it, there shall be no מחשבה to him” implying that at the time when it is offered it can become disqualified, and that it cannot become disqualified on the third day (Sifra, Tzav, Section 8 1). And the following is its meaning (that of the text): At the time when it is offered, this shall not enter the mind of any priest performing a rite with it, to eat of it on the third day, and if he does harbour such a thought, it becomes פגול, an abominable thing,

See here for the Shabbat HaGadol Shiur source-sheet with embedded video.