“We want Moshiach now!” is a declaration, originally part of a song sung by children at summer camps, and endorsed and popularized by the Rebbe. In this refrain we give expression to our most heartfelt desire to see the     unfolding of the Messianic Age through our righteous Moshiach.
When we delve more deeply into this refrain we will discover that the word “now” not only suggests urgency, as the conclusion of this refrain reads, “we don’t want to wait,” but also contains other more subtle messages that tell us what we have to do in addition to ask for and demand Redemption.  One such nuance can be found in this week’s parsha, where the word “now” is used emphatically.
The Biblical word for “now” atah (spelled with an ayin) appears in this week’s parsha: “And now (v’atah) O Israel, what does G‑d, your G‑d, demand of you? Only to fear G‑d, your G‑d, to follow all His ways, to love Him, to serve G‑d your G‑d, with all of your heart and with all your soul.”
The Midrash declares that wherever the word v’atah appears it is always an expression of Teshuvah (repentance or return). In the context of this verse it implies that Teshuvah is a prerequisite for all of which are enumerated in this verse such as fearing G‑d, following all His ways etc. Conversely, for Teshuvah to be a proper Teshuvah, it must be accompanied with all of the things enumerated in this verse. Mere thoughts of repentance do not suffice.
We can now understand the connection of “now=Teshuvah” to Moshiach. In addition to Maimonides’ statement that Teshuvah leads immediate  Redemption, the Zohar teaches us that one of Moshiach’s functions is to inspire and influence  everyone, even the most righteous, to Teshuvah.
The question is how does the ideal of Teshuvah relate to the word “now?”
There are a host of explanations given: One simple explanation is that when one does Teshuvah past transgressions are erased. One is also not held accountable for the sins he or she might commit in the future. As long as a person is sincere in the present, his sins, past and future, are not held against the sinner. Thus, in Teshuvah, one’s status is defined and judged based solely on the present-“now.”
Moreover, as the Chassidic classic Or Hameir explains, even one instant of Teshuvah, one fleeting thought is enough to change one’s status from evil to righteous. This is based on the Talmudic law of a known criminal who betroths a woman stipulating that the marriage will take effect only if he is a righteous person, the marriage is nevertheless valid. The Talmud’s rationale is that he might have had a fleeting thought of Teshuvah a second   before he betrothed the woman. Teshuvah is a process of the moment. Teshuvah can happen instantaneously. While ideally Teshuvah can and ought to be a life-long process, even one instant of Teshuvah has a transformative effect.
The above can be applied to Moshiach. As the Rebbe would state repeatedly, based on the Talmud and Maimonides, even one good deed, word or even thought can change the balance, tip the scales and bring salvation to the entire world. When we say “We want Moshiach Now” it may also convey the message that we can make it happen by one thought.
Another explanation, psychological in nature, is based on a reply the Chassidic Master, Rabbi Chaim of Sanz (known as the Divrei Chaim) gave to a Jew who told him that he “wanted to do Teshuvah.” Rabbi Chaim’s sharp reply to him was: “Then do it now!”
Human nature allows people to feel good about themselves when they make resolutions. On one hand, we find it difficult to leave go of our errant behavior because of the seduction and pressure of the Animal Soul. On the other hand, we have pangs of conscience and guilt which make us feel   uncomfortable. How can we get rid of the guilt without really making    drastic changes in our lives? By making resolutions for the future; putting off our need to change while acknowledging that we must. Hence true  Teshuvah is when we say to ourselves: “now!”
When we say “We Want Moshiach Now!” we must internalize the message that we cannot tolerate even one more moment in exile. While exile is comfortable for some who might feel that they could countenance Moshiach coming a little bit later after they get the most out of exile, the message of the word “Now” is that we want him now, literally! 
Another explanation found in the work Chakal Tapuchin understands the role of the “fleeting moment-v’atah” as the basis and rationale for the  efficacy of Teshuvah.
If we consider the negative impact of a transgression against G‑d it is     difficult to comprehend how we can make amends. The medieval philosopher, Rabbi Yoseph Albo in his Ikkarim explains that G‑d does not judge us according to His infinite stature and standards but with the nuanced understanding that we are ephemeral human beings and judges us accordingly. If G‑d would view us from His vantage point our transgressions would be considered so egregious that no Teshuvah would be effective. The fact that we are so insignificant and temporal “allows” G‑d to accept our Teshuvah.
Hence, the power of Teshuvah lies in our own limited existence; that we live in a fleeting moment, in the state of “now.” The connection to Moshiach is that the reason we want Moshiach now is that we want to proceed from a period of fleeting and temporal existence to a world of permanence; when we will enjoy eternal life, in the physical world.
The LIkkutei Maharan sees the “now” dynamic of Teshuvah as good advice for the sinner who wishes to Teshuvah and turn a new-leaf. One of the impediments to Teshuvah is the penchant some have to wallow in the past. As a result they will always be plagued by guilt and become powerless to extricate themselves from the quagmire of their past. Hence to do effective Teshuvah one must focus on the here-and-now and not on the past.
To be sure, proper Teshuvah does require expressing remorse for past  misdeeds. However, one should not obsess with the past but focus on the present. Indeed, the entire concept of Teshuvah is disengagement from the past and living in the present, beginning with a new slate.
The connection to Moshiach: If “now” means removing the shackles and anguish of the past, the Messianic Age is the ultimate period of saying goodbye to the pain and suffering of the past. Moshiach represents total freedom.
The famous Chassidic master, R. Levi Yitzchak of Berditchev provides a theological explanation for the connectional between Teshuvah and “now.”
Every Jew must believe, Rabbi Levi Yitzchak states, that he or she receives a new surge of vitality every instant. Every moment of life is a new gift from the G‑d without which we could not possibly survive.
Hence, if we truly believe that each and every moment of life we are a new creation with new life, then Teshuvah can be effective, since we are not the same person that sinned. Teshuvah allows us to detach ourselves from the past, Rabbi Levi Yitzchak states, only if we believe that the present is a new life and that in each moment we acquire a new identity.
Moshiach will usher in an age will take this awareness to another level. We will not only continue to believe in the continuous nature of life; we will see it with our own eyes. We will witness the recreation of everything every moment of existence.
The Alter Rebbe, in his Likkutei Torah, provides a Chassidic/Kabbalistic  explanation to the correlation of “now” to Teshuvah. The Alter Rebbe translates the word v’atah as the here-and-now, in contradistinction to the “next world” or the world-to-come, which is the world in which the soul exists without a body. The Alter Rebbe explains that Teshuvah’s ability to transform the negative into positive, “darkness into light” is, paradoxically, an otherworldly dynamic which can only be accessed in our physical world.
In the afterlife, where the disembodied soul is spiritually energized it can only relate to the Divine energy that permeates the world because the soul is unburdened by the physical world and is receptive to these energies. It is not receptive, however, to G‑d’s transcendent energy because it is outside its grasp. By definition, one cannot internalize the transcendent.
In contrast, in our world—the world of “now”—the soul’s ability to    appreciate G‑d’s permeating energy is sharply curtailed because of the obstructing properties of our bodies and Animal Souls. However, precisely because of our “handicap,” we have access to G‑d’s transcendent light, which encompasses us and empowers us to transform the lowliest aspects of our world to the most sublime; darkness into light.
The connection to Moshiach is that contrary to a popular misconception, the Messianic Age will not change our observance of Torah and Mitzvos. It is very much a continuation and completion of our “here-and-now” world. In the Messianic era the soul and body will still work in tandem to transform the darkness into light. The only difference will be the lack of physical and spiritual threats to our lives.
In one way we are unique in that these last moments of Galus/exile  provide us with the greatest   challenges. In the Messianic Age,  notwithstanding the absence of these challenges, we will still be part of the “now” generation, albeit, with enhanced G‑dly awareness and     spiritual growth.