Musar su Salmi 21:4

When Moses asks G–d to appoint a leader for the Jewish people (27,15) that would take his place seeing his death was imminent (27,13), he also asks for the appointment of someone visible now, i.e. יפקד איש. In verse 17, Moses repeats himself asking that this leader should perform two functions which sound alike, i.e. אשר יצא לפניהם ואשר יבא לפניהם, as well as ואשר יוציאם ואשר יביאם. What is the difference between these two requests? Do they not both mean "who will lead them in battle and bring them safely back home?" Actually, the first function of the leader Moses requests is one to be fulfilled immediately אשר יצא לפניהם. The second function referred to, ואשר יוציאם, refers to the ultimate redemption. G–d answered both of Moses' requests by telling him that the leader for the immediate future would be Joshua (27,18). At the same time, G–d showed Moses all the ensuing generations and their respective leaders until the arrival of the Messiah, as we have quoted earlier from the Midrash. He showed Moses how the generations would suffer a continual spiritual decline until the arrival of the Messiah who would be equipped with all the possible intellectual and spiritual attributes. As a demonstration that the decline would set in immediately, G–d told Moses that Joshua would receive only part of his glory, i.e. מהודך, "part of your glory, but not all your glory." The very decline in the quality of successive generations and their leaders leads to the increase in spiritual rejuvenation at the time of the Redemption. An excess of light over darkness will remain until messianic times. This means that the light of the future, the אור חדש, will exceed in intensity the light that had existed at the time of creation, before the original sin, the light which had remained hidden ever since (Bereshit Rabbah 3,6). This subject-matter requires a detailed explanation; it has been touched upon in our commentary on Parshat Balak when we discussed the verse מה טובו אוהליך יעקב (24,5), and demonstrated how the very destruction of the Holy Temple is the cause of the eventual building of an even holier enduring Temple. Due to the increasing diffusion of the pollution introduced into the world by the serpent there was a need for the exile of the Jewish people and the spiritual light in the world kept decreasing. Once wickedness will cease completely, a great light will shine, as we have explained at length in Parshat Balak. This will be further dealt with in the two portions Mattot and Massay. I have devoted a great deal of space there to demonstrate the spiritual value of exile for the Jewish people. The exile experience leads to purification of the Jewish nation, so that the future will bring with it not only a purification of the spirit but also of the physical, i.e. of matter itself. The whole world will become filled with knowledge of [G–d]; everything will be אור, light. I believe that the same approach is correct when we evaluate the gradual spiritual decline of successive generations which is all due to the pollutant the serpent has introduced into the world which infests more and more of our universe. This decline will be reversed in the future and the halachic rule: אין מיעוט אחר מיעוט אלא לרבות, "when we find successive restrictions in the language of the Torah, the purpose is to teach us something of an expansionary nature instead," will apply. Applying this rule to the messianic age when it arrives, this means that the amount of light in the world will exceed even that which existed at the time it began to fade. It is this light which Isaiah (60,1) refers to when he says: קומי אורי כי בא אורך, "Arise, shine forth, for your light has dawned!" It is just because the darkness was so dense that there will be a compensating excess of light.