We find that the Rebbe teaches a firm principle: the flow of the year is a continuum.  This means to say that each holiday or commemoration day is a preparation for the one that follows it on the calendar.  For example: Pesach (coming out of Egypt) is a preparation for Matan Torah on Shavuos; the day of Yud Kislev (the redemption of the Mitteler Rebbe) is a  preparation for Yud-Tes Kislev (the day of redemption 29 years earlier of his father, the Alter Rebbe).  The year that things happened in history is of much less significance than the order that they happen on the calendar.

From this we understand that since 28 Sivan precedes Gimmel Tammuz by 5 days — according to the Rebbe’s principle it serves as a preparation for Gimmel Tammuz.  In what do we see this?  On 28 Sivan we celebrate the Rebbe coming to America, being miraculously saved from the “valley of tears” of war-torn Europe.  Gimmel Tammuz is marks the end of the era (until now, at least) when we could see and hear the Rebbe in the usual ways.  What sort of preparation is this one for that one?

The day of 28 Sivan is noted in the “Shalsheles Hayachas” printed (at the Rebbe’s behest) at the beginning of the sefer Hayom Yom.  It begins with the Maharal of Prague, indicating the 7 generations to the Alter Rebbe.  Then it lists by year the major events and accomplishments of each of the Rebbeim of Chabad, concluding with the Rebbe.  For the Rebbe it states (after the year he was born and married) that in “5701 — Sivan — came to the city of New York”.  Not “arrived” (as a refugee) but “came” (purposefully).  A few comments about the Rebbe’s coming to New York:

Firstly, in the farbrengen of Shavuos 5701, about 10 days before the Rebbe and the Rebbetzin would set sail for America, the Previous Rebbe said:

According to universal custom, preparations for an important guest begin well in advance.  Every corner in the house is cleaned two weeks in advance, the family talks about the upcoming visit, and the neighbors are duly updated. He’s arriving soon. It’s now close to the time when Mashiach will come. It’s time to prepare for his arrival….  

Many see in this a hint to the arrival to America of the Rebbe, Melech HaMoshiach.  The old-timers who were in New York at the time tell that from the moment the Rebbe arrived, “everything changed”.  In fact, the Rebbe even testified on himself that something changed when he arrived to the USA.  At a farbrengen (Chol haMoed Pesach, 5748), the Rebbe addressed his arousal to cry out “Ad Mosai” (“until when” must we remain in golus):

I never heard this from my father, and certainly not from my grandfather. Even from myself, I never heard such talk before I arrived here in the United States…

So even the Rebbe’s impatience for Geuloh started when the Rebbe came to America (on 28 Sivan)!

We could say that 28 Sivan is an aspect of Moshiach being revealed.  Revealed to the Chassidim in America, revealed to the Rebbe himself, revealed in the new activities of Lubavitch that began only after the Rebbe’s arrival.

Based on this, we can see how 28 Sivan is a preparation for Gimmel Tammuz: on 28 Sivan Moshiach is revealed, on Gimmel Tammuz Moshiach is concealed.  As Rashi brings from on Daniel 12:12:

“in the future our Moshiach will be concealed after he has been revealed and will return and be revealed [again]” (שעתיד משיחנו להתכסות אחר שנגלה וישוב ויתגלה)

In order to fulfill the second step of being concealed (with the great value of the Divine service of the period of concealment, as discussed, for example, in the Kuntres of Rosh Chodesh Kislev, 5751 which addresses the concealment of Erev Rosh Chodesh), there must be the preparation of Moshiach being revealed.  The aspect of revelation of 28 Sivan precedes and prepares for the aspect of concealment of Gimmel Tammuz (and it’s connected to Erev Rosh Chodesh, which is the day after 28 Sivan).  Of course Gimmel Tammuz is not an end in itself — it leads to the ultimate redemption of 12-13 Tammuz.  And as the Rebbe says many times: the Geuloh of 12-13 Tammuz showed in retrospect how Gimmel Tammuz itself was “the beginning of the Geuloh”.  May we bring it about now!