The sefer Rozin DeOraisa cites the following teaching from the Apta Rav: Ish ki yidor neder – (30:3)
The Medrash Pelia has a wondrous and puzzling comment, saying that our pasuk is illustrated by the pasuk in Tehillim 144:4: “The days of his life are like a passing shadow”.
The Apta Rav explains the connection between these pesukim by pointing out that when we make a neder (vow) we always say the neder first and Hashem’s name after. Why do we do it in that order? In addition, why do we also use this order when we recite a berocha? When we make a berocha we say Boruch ata Hashem; why do we not say Hashem, ata boruch? In other words, why is Hashem’s name at the end and not at the beginning?
The reason given is that we worry that, Heaven forbid, a person might pass away after having said Hashem’s name, before completing the vow or the blessing. If Hashem’s name were first and then the completion of the neder or berocha and a person then chas vesholom died, he would have taken Hashem’s name in vain because he would not have completed the neder or berocha.
This is what is meant by the pasuk in Tehillim that the days of our lives are as short a passing shadow. We recite a neder in this manner with Hashem’s name at the end of the vow because our days of life pass as a shadow and we worry that a person might die before completing the vow.
This also explains the minhag we have when answering a greeting. Traditionally, we greet each other with “Sholom Aleichem,” so why do we change the order and reply, “Aleichem Sholom”? Why not just answer, “Sholom Aleichem”?
For the same reason, explains the Apta Rav. Sholom is considered Hashem’s name (Shabbos 10b). The Gemora Berochos 6b tells us that the pasuk (Tehillim 34:15) advising one who seeks long life to pursue peace refers to whoever greets his friend first using Sholom. This acts as a guarantee for the one who begins the greeting and says Sholom Aleichem to use Hashem’s name first. However, the responder doesn’t have this great mitzva as his guarantee and must therefore worry just as he who vows or makes a berocha does that he might leave this world. This is why he changes the order and replies, “Aleichem Sholom”, just like neder laShem or boruch ata Hashem, placing Hashem’s name Sholom at the end – just in case. (Yalkut Ohev Yisrael)
