a promise guaranteed to be fulfilled

This Shabbos is my father's yahrzeit.  Al pi halacha, a yahrzeit is a very serious day and a person should really fast.  Everyone these days seems to be sefardi or chassidic and so they mark a yahrzeit with drink and food.  This idea never really resonated with me either emotionally or intellectually; I don't understand how having a meal or a drink is an appropriate way to commemorate someone's passing or what my eating food and saying a bracha does for the departed in shamayim, but what do I know -- to each his own.  Anyway, poskim quote two reasons to mark a yahrzeit: 1) it is a day of kaparah for the departed, who benefits from our charity and Torah study done l'aliyas ha'neshomo; 2) bad mazal - those who are related to the departed should be a little nervous, as the day has proven inauspicious for them.  There is a potential nafka mina l'dina: let's say a person c"v dies at night, but for their relatives on the other side of the world, it is still the previous day.  Is the date of the yahrzeit fixed based on the date where the meis is, or where the aveilim are?  If the point of the yahrzeit is kaparah for the departed, then it should be fixed relative to the meis.  If it is for the sake of the relatives who are alive, to avoid bad mazal, then the date should be relative to their location.  (Other poskim argue that it is not taluy in the reason, v'ain kan makomo).

It seems to me that when yahrzeit falls on Shabbos, then it is exclusively about kavod ha'meis, to enhance the kaparah and aliyas ha'neshomo.  How can Shabbos, a day where וצווחין אף עקתין בטילין ושביתין, be a day with any danger from bad mazal?  

On to the parsha.

At the end of our parsha (23:20) Hashem tells Moshe that he is going to send a malach to accompany Bnei Yisrael.  Rashi comments that Hashem was telling Moshe that Bnei Yisrael were going to sin and therefore he would have to remove His presence, as we read later in Ki Tisa after the cheit ha'eigel: כִּי֩ לֹ֨א אֶֽעֱלֶ֜ה בְּקִרְבְּךָ֗ כִּ֤י עַם־קְשֵׁה־עֹ֙רֶף֙ אַ֔תָּה

Ramban already asks: although after cheit ha'eigel Hashem threatened to send an angel, Moshe was unwilling to accept that decree and davened for it to be abolished, as we read there  וַיֹּ֖אמֶר אֵלָ֑יו אִם־אֵ֤ין פָּנֶ֙יךָ֙ הֹלְכִ֔ים אַֽל־תַּעֲלֵ֖נוּ מִזֶּֽה.  Hashem responded and accepted his plea, גַּ֣ם אֶת־הַדָּבָ֥ר הַזֶּ֛ה אֲשֶׁ֥ר דִּבַּ֖רְתָּ אֶֽעֱשֶׂ֑ה.  Why then would Hashem tell Moshe now about a decree he would threaten in the future but that would never actually come to pass?  Ramban therefore explains that this malach did not appear during Moshe's lifetime.  The parsha is referring to events after Moshe's death, when Yehoshua was the leader, and at that point a malach guided the nation.  

Whether you learn like Rashi or you learn like Ramban, the question that begs asking is what purpose this advanced warning about a malach served.  Why not just wait for the people to sin, and m'meila they would suffer the consequences of being led by a malach?

The Rambam in his introduction to mishnayos zera'im has a yesod that we've discussed before (e.g. here), which the Meshech Chochma brings up every few parshiyos.  The Rambam writes that when G-d makes a promise, it is contingent on the person receiving the promise being worthy of it.  That's why we find that Yaakov Avinu was worried before his encounter with Eisav despite having Hashem's promise of protection.  Yaakov was worried "shema yigrom ha'cheit" -- perhaps he was unworthy of the promise made to him.  However, writes the Rambam, when the promise is articulated by a navi, not revealed by G-d himself, then it is guaranteed to be fulfilled.  If such a promise were to not come to fruition, then people would be liable to question then authenticity of the navi rather than doubt their own worthiness.  To avoid casting aspersions on the navi, the nevuah is guaranteed to be fulfilled no matter what, take it to the bank.  (See Maharal in Gevuros Hashem ch 7.)

This why, explains Meshech Chochma, Hashem appeared to Moshe to tell him that he is giving his bris of shalom to Pinchas, rather than Hashem appearing in a vision to Pinchas himself.  When Moshe said it, it meant fulfillment was guaranteed, irrespective of Pinchas' future merits or chataim.  

And this is why, says Meshech Chochma, when Avraham laughed when he was told that he would have a son, he did not suffer a rebuke from Hashem, but Sarah was rebuked for her laughter. Avraham heard the promise in a vision from Hashem, and he laughed because he doubted he would be worthy of it being fulfilled.  Sarah, on the other hand, heard the promise from a person -- nevuah -- which meant fulfillment was guaranteed.

The Oznayim laTorah explains our pesukim using the same yesod.  Without this parsha, had Bnei Yisrael only had the havtacha of Eretz Yisrael given by Hashem to the Avos, one might have thought that the cheit ha'eigel proved them unworthy of that promise being fulfilled.  Therefore, Hashem gave our parsha to be spoken by Moshe, the greatest navi, so that it would be guranateed that at least a malach, if not Hashem himself, would lead the people into Eretz Yisrael.  Since it was declared by a navi, irrespective of zechuyos, this promise would be fulfilled.  

The parsha is not meant as a besora of sin, a besora of letdown, but to the contrary, it is a guarantee that Klal Yisrael can and will never be abandoned.