The typical purpose of a monument is to remember a person or an incident. Usually it has relevance to the place where the monument is situated. Sometimes, however, a person is so great that a monument is superfluous. Just imagine if you were asked to write under a monument for Moshe Rabeinu— you would be tongue-tied. Most likely, the words “Moshe Rabeinu” would suffice. The Torah and the mitzvos of Moshe Rabeinu are indeed his memorial, and there is no need for a plaque.
Chazal teach us this idea and say:
אין עושין נפשות לצדיקים, דבריהם הן זכרוניהם
We do not make a monument for the righteous, as their words are their remembrance (Medrash Raba 82:10).
Indeed we usually do not find the idea of matzeiva (monument) in regards to the avos hakedoshim. Why then did Yaakov make a matzeiva on Kever Rochel? The medrash teaches us that the reason that Yaakov made a matzeiva was so that when Klal Yisrael would be travelling to Golus Bavel, they would be able to stop by the kever and pray for themselves. Hence the matzeiva was not for remembering Rochel! Instead it was for the bnei Yisrael to know where she was buried so they could pray there at the appropriate time.
Because of Rochel’s selflessness in giving over her simanim to Leah, that zechus will bring about our eventual geula. At times of despair, we go to Kever Rochel to invoke her merit.
Rochel is usually referred to as “imeinu” or even “Mama Rochel.” Why don’t we do the same, for example, with “Mama Sarah”? None of the other matriarchs are referred to as consistently as a “mother” as Rochel is.
It seems to me the reason for this is that motherhood symbolizes self-sacrifice for others: Rochel gave over her husband for others; and she died in childbirth, bringing about the life of her son. The reason why she is called “imeinu” is because she is the embodiment of selflessness.
The churban bayis was brought about through sinas chinam, which has not been rectified עַד הַיּוֹם (Bereishis 35:20). When we go to Kever Rochel to invoke her zechus we should have in mind that selflessness—such as what Mama Rochel displayed—is what can bring about our salvation. Hence הִוא מַצֶּבֶת קְבֻרַת רָחֵל עַד הַיּוֹם is relevant today just as it was at the time of the galus bavel.