Gevurah As Affecting Chesed

Why does Yitzchak's beracha use the name of Hashem associated with דין, the name אלקים, it would seem more logical that giving a beracha is chesed? The Midrash reads into the berachot an allusion to churban habayis and rebuilding, why is this the time to reflect on that? The Midrash also interprets the berachot as a reference to Torah, the Avot already learned Torah, what additional beracha of Torah was Yitzchak giving? Rashi says ויתן יתן ויחזור ויתן, why is there a need to give again, what is lacking the first time? 

The Geamrah Taanis (2a) refers to rain as גבורות גשמים. Rain would seem to be the greatest chesed, why is it gevurah? 

Many Chassidic sources say chesed left unchecked would just give and give and it would cause destruction. It is them middah of gevurah, of dividing the rain into small drops, that keeps the chesed in check (R' Tzadok in numerous places for ex. Amalah Shel Torah #5, see also Be'ar Mayim Chayim Berashis 2.) So too with any infusion of pure giving as chesed, there needs to be the limitation of gevurah to keep in in check from going to far. In this view, it may be suggested that the beracha is given using the name of אלקים, the name associated with גבורות, to allow Yaakov to not be overwhelmed by the beracha. That is the יחזור ויתן, besides giving the beracha itself, it is necessary to give over the kelim to be able to contain the beracha. 

The Rebbe (LS volume 30) says the opposite. We find that Yitzchak, the embodiment of gevurah seems to be associated with chesed in many aspects, (he was born on Pesach, his name is laughter, etc.) How does this align? The Rebbe explains that gevurah is actually a greater form of giving than chesed. Chesed gives someone up to what they can contain while gevurah just gives and gives and hence at times leads to destruction. That is why Yitzchak is associated with extreme forms of joy for he embodies the most extreme form of giving. 

Building onthis principle, the Rebbe explains (LS volume 10) that Yitzchak uses the  name of אלקים to give the beracha because he wanted to give a beracha with greater potential. The beracha was not merely to give the recipient the capability to absorb the berachot, but to internalize them and make it part of his persona. The berachot would not merely be an external power boost but become part of the makeup and avodah of Yaakov himself. The beracha of Torah is the beracha not just to be able to intuit the teaching of the Torah as the Avot did but to be able to work in the learning of Torah and to make it part of the makeup of Yaakov. That is also why there is the allusion to the destruction and rebuilding of the Mikdash for the ability to become a baal teshuva, to have to work on one's self to fix and mend their ways, is something that is being conveyed in the beracha as well. That is the יחזור ויתן, the capability to incorporate the beracha as part of Yaakov's own self.