What’s the Connection?
The Midrash connects the opening words of this Parsha, “Speak to the children of Israel, that they shall take for Me an offering…” with the response the Jewish people gave when they were offered the Torah.
“When the children of Israel said, “We will do and we will hear” [in response to G‑d’s offer to give them the Torah], G‑d then said “take for Me an offering.”
Their submission to G‑d’s will even before they knew what it was stood them in good stead. The Talmud relates, they were rewarded with two crowns, “One for saying, we will do and one for saying we will hear.”
We must try to understand what the connection is between the Jewish people’s reversal of “doing” before “hearing” and the command for the Jewish people to contribute towards the construction of the Mishkan, the portable Sanctuary in the desert.
Commentators explain that G‑d, in response to the Jewish people’s unconventional approach to Torah, followed suit and reversed the command to contribute to the Mishkan and the purpose of the Mishkan.
When G‑d told them to contribute their gold, silver etc., He did not tell them the purpose of these contributions. Only later G‑d provided that information, when He stated, “They shall make for me a Sanctuary and I will dwell among them.” Moses understood that first he had to ask the Children of Israel to contribute their wealth, and only afterwards tell them how it would be used.
The unconventional response of the Children of Israel at the Giving of the Torah (“we will do and we will hear”) elicited a reciprocal unconventional response from G‑d. G‑d was convinced that the Jewish people did not need to know the reasons for their contributions. As long as G‑d asked for it, the assumption was that they were prepared to give it.
We still have to understand why G‑d had to reverse the order. Didn’t G‑d know that the people would have contributed to any cause that G‑d supported and advocated even without knowing the purpose of that cause? Why did He have to test them when they had already demonstrated their unconditional devotion to G‑d?
The Anatomy of a test
The simple answer is that this question we must first understand the meaning of a test given by G‑d. A test is not intended to determine one’s level of commitment. The word for test in Biblical Hebrew is nes, which is the same word for miracle. The common denominator of a test and a miracle is that they both transcend the natural order. A miracle defies the nature of the world and a test elicits an unconventional surge of the soul’s energy that empowers us to break out of the constraints of our own nature.
 While the Jewish people demonstrated their ability to rise above their nature when they said “we will do:” before “we will hear,” G‑d gave them another opportunity to rise even higher.
The question still remains. What difference is there between these two tests? Aren’t they basically identical?
General Versus Specific; Abstract Versus Concrete
Upon reflection we can discern several differences between the general idea that they were willing to observe the entire Torah without knowing what is in it and contributing to a holy cause without knowing what is the cause.
First, when we are given a general, theoretical challenge, there is less room for resistance to it relative to the resistance we may feel when we know precisely what we are told to do.  It’s relatively easy for us to be magnanimous and idealistic when speaking in theory. However, when we receive a specific and concrete command do to something that might be against our nature, there can be greater resistance.    Yet, here too, the Jewish people demonstrated that they were willing to submit to a specific and concrete command to part with their wealth for an unknown cause.
A Mountain of Love Over Our Heads
Second, the Talmud states that G‑d placed the mountain over the heads of the Jewish people and coerced them into accepting the Torah. Commentators raised the question how that can be reconciled with their declaring “we will do” even before they heard what was in the Torah. Why then did G‑d have to compel them to accept it?
Chassidic thought provides the following answer:
The mountain placed over their heads is a metaphor for the love G‑d had showered upon them. G‑d performed all these incredible miracles in Egypt; freed them from slavery, took them out of Egypt and provided for their every need in the desert. How could they say no to G‑d’s offer of giving them the Torah? Indeed, in Midrashic sources the mountain is described as their Chupah, the wedding canopy. The people were so overwhelmed with the love they experienced from G‑d that they enthusiastically embraced the Torah even before they knew what was in it. They had no real choice.
Let’s compare this with the command to contribute for the construction of the Mishkan. According to one opinion, this occurred after they worshipped the Golden Calf and undermined the love relationship between G‑d and the Jewish nation. Indeed, the Torah records how G‑d expressed His desire to destroy them and start over again with Moses’ progeny. In this period of separation it was indeed a greater test for them to embrace G‑d’s command.
Moreover, if they knew at the outset that their contributions were intended for the construction of the Mishkan in which G‑d would return to dwell among them and have their loving relationship restored, it would have been easy for them to comply with this command. , Asking for the contributions without stating the cause might have caused the Israelites to believe that G‑d was actually asking them to divest themselves of the wealth, thus reversing the entire process of the Exodus through which G‑d chose the people with love and awarded them great wealth.
Thus, complying with this command now, it constituted a far greater test of faith and commitment than their saying “we will do” before “we will hear” when their loving relationship with G‑d was intact.
“Take it For My Name”
A third approach to the uniqueness of contributing to the Mishkan without initially knowing that it was for the Mishkan relates to the condition attached to their contributions. The Torah states, “…And they shall take for Me an offering.”
Commentators note that it does not say “they shall give Me an offering,” but rather “they shall take…”
In addition, the words “for Me,” Rashi explains, implies that their giving shall be in His name.
What do these two provisions suggest?
There are two ways one can perform a Mitzvah. The first is for us to respond to a command from on High and give and submit ourselves to the will of the Commander. In this mode, it doesn’t require that we develop an understanding of and appreciating for the Commander. We don’t have to know His name; His characteristics and attributes. It requires only the commitment to give and submit to the Commander who is above and beyond us.
There is, however, a second approach to giving: It is when we identify with the Commander and appreciate His role as it is reflected through His name. The name identifies certain Divine attributes associated with the command; when appreciated it deepens our commitment  because it allows us to internalize the commandment.  
With this approach we are not just giving we are also receiving because we have internalized the contribution and empowered it to uplift us, which is the simple translation of the word Terumah, which is usually translated as offering.
This explains what was unique about the reversal of the test of not knowing the cause for which they were told to contribute,.
Had they known the cause, it would have been much easier for them to internalize the value and the importance of their contribution to the Mishkan.  
Not knowing, initially, what the cause was, they went beyond just giving in response to a command from an unknowable and inscrutable G‑d. They actually internalized it and felt that they were receiving as much as giving.
To summarize:
By G‑d first telling them to give and afterward revealing the cause for which they had to give, was unique because:
a) It was not just some amorphous, theoretical cause; it was a specific command to give of their wealth, without knowing for what purpose.
b) This command came after their loving relationship with G‑d was shattered by the sin of the Golden Calf. Yet, it did not weaken their dedication to give without even knowing for what and why they were giving.
c) They were asked not only to give but also to take, absorb and internalize their giving, without the luxury of knowing for what and why.
Preparing for Moshiach and Redemption
As the Rebbe told us, we are living on the very threshold of the Messianic Age. The Messianic Age will bring about the building of the Third Bais Hamikdash; the conduit for G‑d’s revelation throughout the world. 
We are asked to contribute towards this objective by the Mitzvos we do now.
Our Mitzvah observance will be ideal and complete when we apply the foregoing three points:
First, we must not just hope and wait for Moshiach in a general, non-descript fashion but commit ourselves to specific actions that hasten and prepare us for the Redemption, such as giving tzedakah and learning the parts of Torah that deal with Moshiach and Redemption.
Second, even when it seems that Galus conditions and attitudes define our lives and our relationship with G‑d is wanting, we still will give of ourselves unconditionally as if we are in the state of Redemption.
Third, and equally important, we do not just give and submit without feeling. We must allow the light of Redemption to enter into our consciousness, our minds and hearts, and fully internalize its energy.