The Mishna (Taanis 26a) bases the idea of Anshei Maamad on the passuk in our parsha in 28:2.
אלו הן מעמדות לפי שנאמר צו את בני ישראל . . את קרבני לחמי וכי היאך קרבנו של אדם קרב והוא אינו עומד על גביו התקינו נביאים הראשונים עשרים וארבעה משמרות
אי אפשר שיהי' קרבנו של אדם קרב והוא אינו עומד על גביו וקרבנות הציבור הן קרבן של כל ישראל ואי אפשר שיהיו ישראל כולן עומדין בעזרה בשעת קרבן לפיכך תקנו נביאים הראשונים שיבררו מישראל כשרים ויראי חטא ויהיו שלוחי כל ישראל לעמוד על הקרבנות והם הנקראים אנשי מעמד
But Rashi in our parsha brings from the Sifri a slightly different limud,
צו את בני ישראל ואמרת אלהם: את קרבני לחמי לאשי ריח ניחחי תשמרו להקריב לי במועדוRashi-
תשמרו - שיהיו כהנים ולוים וישראלים עומדין על גביו מכאן למדו ותקנו מעמדות
The Sifri inside says
תשמרו שיהו כהנים ולוים וישראלים עומדים עליהם
ד"ה וישראל במעמדן... עומדין על תמידי ציבור בשעת הקרבן כדתנן במסכת תענית תשמרו להקריב לי במועדו היאך שומר אם אינו עומד על גביו תיקנו נביאים הראשוניםSotah 5a
ד"ה אקורבנייהו...ומצוה על האדם שיעמוד וישמור על קרבנו ונפקא לן בסיפרי מתשמרו להקריב לי במועדו '
The Rav in Mishnayos in Taanis adds an interesting thing, that the mitzva of Shmira is to watch the Kohanim doing the avoda.
תשמרו להקריב לי במועדו לישראל מצוה שיעמדו על הכהנים בשעת עבודה
So let us assume there is a fundamental distinction between the way the Rambam and Rashi learn the din of Maamad. The Rambam says this din requires the presence of the baal hakorban; Rashi learns that the din requires that the baalim do "shemira" during the hakrava.
The Tur (YD 265) brings from the Baal HaItur that the father should stand near the Mohel during the Bris, because it wouldn't make any sense for one's korban to be brought without him there. This is also brought in the Mechaber in 265:9.
מנהג שאבי הבן עומד על המוהל להודיע שהוא שלוחו כדאמרינן לגבי קרבן אפשר שיהא קרבנו של אדם קרב והוא אינו עומד על גביו
שו"ע שם סע' ט'- אבי הבן עומד על המוהל להודיע שהוא שלוחו
שו"ע שם סע' ט'- אבי הבן עומד על המוהל להודיע שהוא שלוחו
The Sifri needs explanation. Bishlema according to our Mishna and the Rambam who brings our Mishna verbatim, it applies specifically to korbanos. וכי היאך קרבנו של אדם קרב והוא אינו עומד על גביו. Bris Mila, as Zohar mentions and Rabbeinu Bachya ( בראשית י"ז, יג) elaborates upon, is like a korban, since blood is spilled in the process, and, neither may be done within eight days of birth.
מצות מילה היא כענין קרבן וכשם שדם הקרבן לכפרה על המזבח כך דם המילה מכפר וע״כ מצותה ביום השמיני כי הקרבן לא יכשר עד יום חBut according to the Sifri's drasha that there is a new din of Shemira, what is the idea of Shemira? What is added to the kiyum hamitzva by doing Shemira? If shlichus helps, then it helps. Even assuming there's a concept of מצוה בו יותר מבשלוחו by mitzvos other than preparation for Shabbos and kiddushin, why isn't this applied to other mitzvos, like hafrashas teruma; and more fundamentally, would standing there mitigate that problem of מצוה בו יותר מבשלוחו?
(Harav Dovid Oppenheimer of Chicago proposes that in shlichus in general, there is a chkira among the achronim whether it is considered the act of the baalim or the act of the shliach; see section on Shelichus in Sefer HaZikaron for Reb Chaim Shmuelevitz. If the baalim is standing there, he suggests, everyone would agree that it is considered the act of the baalim, just as the Gemara in Gittin has a hava amina that if chatzer is a yad, it needs to be next to the woman. I'd like to offer a different pshat.)
Let us think for a moment about the Tosfos Rid in Kiddushin 29a. The Gemara has a passuk to teach that the obligation to perform mila on one's child only applies to the father but not the mother. All the rishonim ask, but it's a zman grama, so the passuk is not necessary. Tosfos Rid answers that if the mitzva on the parent was simply to do an act of milah, since that act is time-related, it would be called Zeman Grama. But the obligation on the parent is to see to it that the milah is done. The obligation of "see to it that it gets done" is not time-related. It begins when the child is born and goes on every moment of the day and night until it actually takes place. This Tosfos Rid is remarkable for many reasons, among which is that this logic ought to apply to every single zman grama- although tefillin is only on a weekday, the obligation to see to it that I have and wear tefillin is constant, and the same for lulav and shofar. Additionally, it is amazing that where the act of the mitzva milah is Zman Grama, and would exclude women, that the seemingly more vague and distant obligation to "see to it that it gets done" would be not zman grama and therefore not exclude women- that it would create a greater obligation.
In any case, you see that the Tosfos Rid learns that Milah is different in that it has a defining characteristic that it creates an obligation to see to it that it's done, not only an obligation to do it. I believe that the Sifri is applying that logic to Korbanos. The Torah does not merely obligate Klal Yisrael to bring korbanos via kohanim. They are obligated in a din of תשמרו, and תשמרו creates a new obligation to see to it that it's done. It's not enough to pay for it, it's not enough to book the best kohein. תשמרו means that you yourself have to ensure that it's done and that it's done right.
This concept of תשמרו creating a higher level of obligation can be seen by Matza Shmura as well, to the extent that there used to be a minhag to moisten the grain- לתיתה- before milling so that the watchers would have a chance to be vigilant to ensure that no chimutz would result. Pesachim 35a- אמר רבא מצוה ללתות, שנאמר ושמרתם את המצות, אי לא דבעי לתיתה, שימור למאי.
For Milah and Matza Shemura and Avodas HaKorbanos, Due Diligence is not enough. For these Mitzvos the Torah requires Due Vigilance.
I was zocheh to attend a bris mila this week. My daughter and son in law named their new son Aharon Tzvi after my father zatzal. One clear character trait of my father was ameilus, and this was known by every one of his chavrusos and business associates and lawyers and employees. When he decided something needed to be done, he did it בלב ונפש. He would follow it to the very end, and not rely on anybody. He could have the best lawyer in Chicago draw a contract or a mortgage, but he would go through it line by line and would often point out important modifications that the lawyer immediately incorporated into his practice. When he gave tzedaka, he would make sure that it got to the right person and that it was used in the right way. It goes without saying that when he learned, he learned בלב ונפש. My father learned with Reb Leizer Platzinsky for most of his thirteen years in Slabodka. Reb Leizer's grandson bumped into my son in Yerushalayim, and told him that his grandfather told him that at one point, he and my father shared a room. Reb Leizer was the Alter's grandson, and he was a yachson in the yeshiva, so he had a comfortable bed. But my father davka slept on the floor, because he decided that if he slept in a bed and was comfortable, it would be harder to get up early to learn. That is a level of dedication and Ameilus BaTorah that inheres to the concept of תשמרו. May Hashem give us siyata dishmaya to see Aharon Tzvi and all his siblings and cousins do their avodas Hashem with that level of Ameilus.
Here is big brother Akiva holding Aharon Tzvi שיחיו עד ביאת משיח צדקנו
Aharon Tzvi wore a cotton kimono at his bris. Lo these many years ago my mother made it for me and I wore it at my bris, and my kids wore it at their brisos, and theirs wore it at theirs. It's not the Aderes Eliahu, but it's a nice family tradition.