I appreciate the point about the world having a goal and destiny and how the world is evolving towards a state of perfection and redemption. But why the focus on a human being as the redeemer? If redemption is that crucial, couldn't G‑d do it on His own?
In typical rabbi fashion let me explain with a parable.
I've recently noticed that mortgage brokers are sprouting up all over the place. More and more people prefer to use mortgage brokers rather than the old-fashioned system of setting up an appointment with their bank. The reason? With so many different loans and lenders in the market, it's highly advisable to rely on a mortgage broker to do the legwork for you. With a broker you have access to a greater range of mortgage options, better service and you can use the broker to negotiate with lenders on your behalf. The banks also benefit from this trend, as they can now conserve manpower by outsourcing to the brokers the task of finding and qualifying borrowers. Most importantly, the broker "understands the language" of both the lenders and the clients. Thus, the broker acts as a successful intermediary.
No one else other than us can do the job. All others have a "conflict of interest"...What would happen if it was discovered that a mortgage broker is actually an employee of a particular lending institution? That's what we call a dishonest broker. He would lose his license and possibly be culpable for a variety of legal penalties. It would be like two conflicting parties finally agreeing to mediate, only to discover that the designated arbitrator has a direct financial or personal interest in the outcome of the arbitration.
Same thing with Moshiach. Our duty is to create a union between the world's material substance and its spiritual reality, to marry Heaven and Earth. Call it arbitration, negotiation, brokerage or match-making. We have been entrusted with the sacred mission of perfecting this world by bringing spirituality and G‑dliness into an otherwise ungodly world. Our observance of the mitzvot all center on this ideal of bridging the chasm between G‑dliness and Worldliness. Every time we engage in the physical act of performing a mitzvah we speed up the process of "drawing down" the Divine into our environment.
No one else other than us can do the job. All others have a "conflict of interest" and represent one of the two parties. Who do you propose to use as the negotiator between both parties? G‑d? He, as it were, can't do it on His own. He's representing one of the parties...
We, on the other hand, possess a soul which is "part of G‑d above," yet this G‑dly soul is garbed in a physical and corporeal body. We "understand the language" of both parties and are therefore the perfect candidate for the task of merging the two.
The consummation of this process will be realized in the Era of Redemption when every dimension of our worldly existence will be truly permeated by G‑dliness. In the words of our Sages: "Currently we are in a state of betrothal; in the World to Come—will be the Marriage."
Moshiach, the one who will usher in the redemption, is a "man of this world," a flesh-and-blood human being who undergoes physical challenges such as stress, opposition and health-considerations. Yet, his soul is as pure and pristine as they come. He will have nullified his ego and intellect to be consistent with the Divine will. He has a good take on both Heaven and Earth.
Indeed, an honest broker.