From a non-Chabad source (I believe)...
http://www.torah.org/learning/olas-shabbos/5762/tazria.htmlParshas Tazria-MetzoraRabbi Eliyahu HoffmannLiving for the Moment
It is said that Mashiach lives in every generation, waiting patiently for the message that the time has come to reveal himself. Now this may sound like a silly question, but where exactly does he reside in the meantime?
In fact, the Gemara (Sanhedrin 98a) describes an encounter between Rabbi Yehoshua ben Levi and Eliyahu HaNavi, during which Rabbi Yehoshua ben Levi asked Eliyahu this exact question:
Said Rabbi Yehoshua to Eliyahu: "When will Mashiach come [i.e. reveal himself]?" Said he: "Why don't you go and ask him?" "And where is he to be found?" "He sits among the lepers at the gates to the city of Rome." "How will I know which one is him?" "You will see," said Eliyahu, "that the other lepers remove their bandages and clean their wounds all at once, while Mashiach removes them one at a time."
Rabbi Yehoshua went. He said, "Shalom Aleicha - Peace to you my teacher, my mentor." "Peace to you, son of Levi." "When are you coming?" asked R' Yehoshua. Mashiach said: "Today."
Later, R' Yehoshua once again met Eliyahu. "Nu - Did you find Mashiach?" "Yes. He lied to me. I asked him when he was coming, and he told me, 'Today,' [yet he never came!]." Said Eliyahu, "Today - if you will heed My voice (Tehillim/Psalms 95:7)"
Obviously there is more to this story than meets the eye. Why is Mashiach depicted as a leper? And why, while the other lepers cleanse their wounds all at once, does he clean his individually? And why did he "trick" R' Yehoshua ben Levi by telling him he was coming "Today?"
The Gemara (ibid.) describes two possibilities as to when Mashiach will come: If we will merit his revelation through good deeds and repentance, he could come at any moment. Otherwise, we must wait until the appointed time. It's kind of disheartening: If Hashem awaits the day that we will attain perfection, what chance do we stand? If earlier generations, who dwarf us with their Torah, their mitzvos, their purity, and their fear of Heaven, did not succeed in achieving "Today - if you listen to my voice," then what hope is their for a generation such as ours? As someone once quipped: "If that's the case - we might as well make ourselves comfortable, because it's going to be a long ride..."
A great tzaddik once mused: Every Jew, given the choice, would in a heartbeat do teshuva (repent) right now, today. What is it, then, that prevents him? Yesterday and tomorrow. He worries about yesterday's mistakes and blunders, and frets over what tomorrow will bring. Were it that he would focus only on today, on this very moment, nothing could stop him.
"Living for the moment" is a term that carries with it a negative connotation. In fact, living for the moment is the key to success in serving Hashem and overcoming our faults and deficiencies. Taken as a whole, life is a daunting proposition. There are children to raise, careers to advance, mitzvos to do, weddings, bar mitzvahs, simchos, learning, davening, flossing our teeth... Give life too much thought and you'll never get out of bed in the morning.
The trick is to live for the moment. While it is true that there are thousands of things to do - hills to climb, valleys to conquer - the only thing we truly control is this very moment. There is a famous saying (which has become a song): "The past is gone; the future not yet; the present like the blink of an eye."
Perhaps what Mashiach meant by "Today" was that blink of an eye; the fleeting moment we call the present. Hashem does not ask that we build Him great castles. Just simply give Hashem your now - your today. Do not worry about what has been - it is of no significance now. What tomorrow will bring - you will see then. Give me your today, says Mashiach, and I will come.
Now this does not mean that we should recklessly lunge through life, with complete disregard for past deeds and no concern for our future welfare. What it does mean is that we internalize the reality that with all our planning and ambitions, all we really are capable of controlling is what we are doing right now. If you are assessing your past, do it with the realization that you can't change anything that has already been done. What you can do is change your present, with an awareness of past blunders. Plan for the future, but don't let anxiety about tomorrow - which is ultimately beyond your control - detract from what you can do today.
Mashiach as a leper is symbolic: Just as a leper must live in quarantine, removed from his home and his family, so too, as a result of our sins, we are in exile from our homeland, and have had the Holy Temple removed from our midst. While others think that it is necessary to care for all their wounds at once, Mashiach dresses one wound at a time. This is his message: "Hayom - Today, if you listen to My voice." Do not attempt to address all life's difficulties at once, for you will falter. Address issues as they arise, live each moment to its fullest, and do the best you can right now. Tomorrow is another day; there will be other battles to wage, other territories to conquer.
While we are no doubt (at best) dwarfs relative to our ancestors, perhaps in this one regard we stand a better chance than them. Everyone bemoans the fact that we live today in the "generation of the disposables," where everything in life is throw-away (tableware, diapers, relationships...), and precious little remains of permanence and substance. While we must take care not to "live for the moment" in the sense of caring only about satisfying momentary whims and desires, perhaps living in such a society makes us uniquely suited to follow Mashiach's advice to concentrate on giving Hashem our "Today," and not getting bogged down by yesterday and tomorrow.
Deep within the recesses of every Jewish soul burns a flame, yet sometimes the light of that flame becomes obstructed by the oppressive concerns and worries of life. By "living for the now," we can remove those obstructions, and allow the flame of the neshama to warm our lives and the lives of those around us. Have a good Shabbos.