From this week's Torah portion, Beha'alotcha.

In 1943, the previous Lubavitcher Rebbe, Rabbi Yosef Y. Schneersohn, of blessed memory, issued an urgent call to Chasidim to begin a massive campaign establishing additional religious institutions around the world. Many people could not understand why the Rebbe was initiating such a large-scale operation if, as the Rebbe had stated, we could hear the approaching footsteps of Moshiach. Would not such an undertaking constitute an enormous waste of effort if the Jewish people are to return to Israel with the coming of Moshiach?By way of explanation, the Previous Rebbe referred to a teaching derived from this week's Torah portion, Beha'alotcha.
"At times, the cloud remained from evening till morning; and when the cloud was taken up in the morning, they journeyed forward. .. at the order of G-d they remained in the camp, and at the order of G-d they journeyed forward."
For forty years, the encampments of the Jewish people as they journeyed through the wilderness towards the land of Israel, were of varying duration.
They ranged from a short overnight stay to a nineteen year period in the same location. Yet, at each site, the Sanctuary was erected and offerings were brought.
Why was it necessary to expend such massive effort even for those encampments that were destined to last only a few hours?
Erecting the Sanctuary, just like the journeys themselves, was done solely according to G-d's command.
It therefore matters little whether the Sanctuary stood for many years on the same spot, or whether it was erected for just a few minutes.
The physical object used in the performance of a mitzva is significant solely because such is the will of G-d.
In this case, the mitzva to erect the Sanctuary, for whatever length of time G-d desired, is what imbued the labor involved in its erection with meaning.
The Jewish people, "believers, the children of believers," have faith in the coming of Moshiach and await his arrival each and every day.
Yet this fundamental belief in no way contradicts our efforts to build up and strengthen Jewish life and institutions while we are waiting. G-d wants us to take an active role in imbuing our surroundings with holiness no matter where the exile takes us, for this is His will and an integral part of Divine Plan.
We needn't worry that Moshiach's arrival will interrupt us in the first stages of whatever worthy project we are currently involved in; when Moshiach comes, we will fully understand the significance of all our service throughout the thousands of years of exile, even those that have not yet been completed.

Adapted from a talk of the Rebbe, 19 Kislev, 5717 (1957)