The Talmud Taanit (near the end) lists 5 historical reasons to highly celebrate TuBav (15th of Av) in contrast & soon after the dark sadness TishaBAv:
(1) it marks when generation of desert stopped dying before entry to Israel (2) tribes were granted permission to marry one another (3) its the day then northern kingdom removed border guards to allow for the unified Temple pilgrimage (4) those killed by Romans at Beitar were finally allowed burial (5) the last day to gather wood for Temple altar before the hot summer season began to shift cooler.
It’s because of (one or more, or all of) these 5 reasons and the mood & vibe of the day, that there was a festive air & the daughters of Jerusalem would borrow white garments from each other (so as not to shame one who didn’t have of their own) & dance in the vineyards & call to suitors to set their eyes on values which they valued. Hence Tu B’Av is known for its matchmaking or shidduchim, a time for love and connection.
The Rebbe seeks (as Rebbe often does!) to find a unifying connection between these 5 historical reasons and in Rebbe’s way sees unifying connection in the focus on removing barriers to going forward in connection to be the underlying theme of everything TuBAv & what sets it so apart in contrast from TishaBav.
Some of the five are obviously about removing barriers or furthering connections but some take more study to realize that but suffice it to say that we ought to act on doing whatever possible to minimize barriers to connection and highlighting, celebrating & making more & deeper connections!