The flow of the Gemara seems quite clear that tears constitute a double-edged sword. On the one hand, one causing someone else pain to the point of bringing him/her to tears can have quite a detrimental and negative effect, invoking the midas hadin against the perpetrator. On the other hand, one who sheds tears while praying can invoke the midas harachamim much more so than with just prayer alone.
In fact, the Maharam Shif remarks there, that he is somewhat puzzled by why we say in Selichos, “Machnisei dimah hachnisu dimoseinu.” “Angels of tears bring in our tears.” After all, tears are so powerful and are granted immediate access to Heaven, why should we need to ask the Angels to bring our tears into G-d?!
The power that tears can have is further illustrated in the Gemara (Kesuvos 62b) which relates the incident in which Rav Rechumei would learn in the Yeshiva of Rava the whole year and would leave to visit home once a year on Erev Yom Kippur. One year he became so involved in his learning that he delayed in coming home. His wife was anxiously awaiting his once-yearly visit and when he did not arrive at the expected time, she shed one tear. As a result, the attic in which Rav Rechumei was sitting at the time, collapsed and Rav Rechumei died instantly.
Now, surely Rav Rechumei’s wife did not want him to die and was certainly much more hurt by her husband being taken away from her altogether, than by his just coming home later than the usual.
Nevertheless, R’ Chaim Shmulevitz (Sichos Mussar: Maamar Zechiras Miriam) explains, such is the power of tears. When one causes another person pain to the point of tears, it is likened to a fire which burns on contact, regardless of what the intent was. Just as fire burns on contact, whether it was started intentionally or not, so too causing another person pain to the point of tears can invoke an immediate and harsh response from Heaven, even if done unintentionally, Rachmana litzlan.
Additionally, we find that as soon as Basyah heard Moshe crying as a baby in the Nile River, she was immediately filled with compassion and came to his aid. The pasuk (Shemos, 2,6) says “Vehinei naar boche vatachmol olav.” “Behold the child was crying, and she had pity on him.”
The Zohar remarks that this terminology alludes to this concept that crying is very powerful and can achieve results much more effectively than prayer without tears. Based on this the Ari, z”l advised that one should do his utmost to shed tears during the closing prayer of Neilah on Yom Kippur, since tears are so very powerful and G-d will certainly not ignore them.
The Yalkut Me’am Loez (Toldos 27,38) quotes from the Zohar that in the merit of the tears that Eisav cried while he was asking Yitzchak Avinu for a bracha, that the Jewish nation has now been under Eisav’s rule for so long. And the Jews will remain under his control until they do repentance, likewise, with tears invoking G-d’s compassion.
Not only that, but the Medrash (Tehilim 137) says that when Yirmiyahu was being separated from the Jewish nation right after the Churban, they began crying that they wanted him to stay with them. Yirmiyahu responded that if they would have cried even one time prior to the Churban, back when he was imploring them to do teshuva, they would not have gone into exile. Such is the power of crying.
We see from Leah, as well, the power of davening with tears. The pasuk says “The eyes of Leah were weak from crying.” And Rashi explains that this was so because Rochel was originally supposed to marry Yaakov, and Leah was supposed to marry Eisav.
The Gemara, Bava Basra 123a, relates that we see from here how powerfully effective prayer with tears can be. Through crying, Leah altered the gezaira of bas ploni leploni, i.e. who she was to marry. Not only that, but she married Yaakov even before his original bas zivug, Rochel, did. Even more Rochel’s son Yosef was really supposed to be the firstborn of Yaakov. Instead, Leah bore Reuven first, making her son the firstborn of Yaakov, as well as the first shevet, a direct result of the power of prayer accompanied by tears.
