These days it’s popular to poo-poo things like brachos. The argument is that just running to a rebbe to get a bracha is not going to have any effect unless you do teshuvah. There certainly in truth to that idea – a mystical quick fix cannot replace the hard work of avodah. And yet, we see that Eisav, someone certainly not interested in avodah and teshuvah, got tremendous credit simply for his belief in the power Yitzchak’s blessing. Surely someone who goes to a rebbe because he/she believes in the power of a tzadik’s bracha deserves no less.
Rashi comments on the bracha given to Ya'akov of “V’yiten lacha Elokim m’tal hashamayim” that “yachzor v’yitein,” return and give again. Can’t Hashem give the bracha all in one shot? Of course he can, but the point is to forge an ongoing relationship.
This is the difference between the bracha given to Ya'akov, "V'yiten lecha Elokim m'mtal hashamayim u'mishmanei ha'aretz," and the bracha given to Eisav, "M'shamnei ha'aretz y'hiyeh moshavecha u'mtal hashamayim m'al." Both refer to the blessing of tal and the fat of the land. What seperates the two is that word "v'yitein." Ya'akov is cognizent that bracha has a Giver -- it's not "y'hiyeh," something that just happens. That relationship with the One who gives bracha is what is so special.
As we've discussed before, the real gift of the "v'yiten lecha" is "...Elokim," G-dliness. "M'tal hashamayim..." is just the heichi timtzah, the context which makes it a little easier to discover G-d.
The Sefas Emes suggests that “yachzor v’yitein” is a charge to Ya’akov, the recipient of bracha, not to horde what he receives, but to use it to grow and enable others to grow in their avodas Hashem. When you utilize the bracha you have been given in that way, there is a “yachzor v’yitein” of more bracha because you have made the world a kli capable of receiving more. "V'yiten" is then an ongoing cycle, not an event.
The gemara in Ta’anis writes that the difference between dew and rain is that rain sometimes falls and sometimes doesn’t. In NY last year we had a hurricane; this year we are on the verge of drought conditions because it hasn't rained. Dew, however, is always is there. So why does Ya’akov need a bracha for "tal," something that’s always there? The Shem m’Shmuel by tefilas tal writes that precisely for things that are always there we need a bracha to remember that it’s “yiten lecha *Elokim*,” that it all comes from Hashem.