In the aggadata part of the shiur, HaRav Weiss, ShliT"A, expounded on the Chazal in Nedarim and Bava Metzia that explains the pasuk,
דאמר רב יהודה אמר רב מאי דכתיב מי האיש החכם ויבן את זאת דבר זה נשאל לחכמים ולנביאים ולא פירשוהו עד שפירשו הקב"ה בעצמו דכתיב ויאמר ה' על עזבם את תורתי וגו' אמר רב יהודה אמר רב שאין מברכין בתורה תחלה
He asked, what kind of reason is this for the destruction of a nation? Weren't they guilty of the most serious transgressions of Murder, Idolatry, and Immorality? Wouldn't that far outshadow the mere neglect to say Birchas HaTorah?
Rav Weiss offered a number of explanations.
The first was based on the following parable that was sourced in the writings of the Alshich:
A King had a favorite musician whose music would consistently soothe the pressures of the King. The King was very much dependent on this musician for his peace of mind. One time the musician was caught in the act of treason and was brought to trial. He was clearly guilty of a capitol offense, yet the KIng interfered on his brehalf. Of course he is liable for execution, but I cannot find another musician of his caliber. His execution will severely effect my well-being. Based on the King's plea, the court suspended his sentence.
A while later, the musician sustained a serious injury and was no longer able to produce his music. He was no longer able to soothe the King's tensions. As such, the King said, "He no longer provides the music that I need, let the death sentence be carried out."
In truth, the infractiions that made us liable for the destruction were the cardinal sins that were constantly being committed. Still, for as long as there was torah L'Shma that provided the King with sweet music, the sentence was suspended. However, when the music of Torah study ceased and the Jews were no longer makibng birchas HaTorah, their grace status was terminated and the decree of destruction was reinstated.
In this explanation HaRav Weiss, ShLiT"A, wanted to say that of course the destruction was due to the commission of the three cardinal sins. What the Navi wanted to ask is how could the Jewish people lose their "moral compass" to the extent that they sank into the morass of these most terrible transgressions?
To this the Navi answers that "they have forsaken my Torah". But this is not satisfactory because the Jewish people definitely were learning Torah. Rav Yehuda has explained to us that the problem was that they did not say Birchas HaTorah first. What is the meaning of this in relation to the three cardinal sins?
There is a difference of opinion as to exactly which of the Birchos HaTorah was neglected. The Taz says that the intention is for the first Bracha of "la'asok b'divrei Torah". Like this opinion, the explanation is that even though they learned Torah, they did not make learning Torah their "esek", their occupation. It was just something that they learned willy-nilly for intellectual stimulation, but not as a guidebook for life that is to be applied in practice. as such, they couldn't sincerely say the blessing of La'asok b'divrei Torah (even if they physically did so). As it was not dsomething that they put into full time practice, they emulated the ways of the nations and stumbled into the cardinal sins.
The Baal Shem Tov differs with the Taz and says that the bracha that was neglected was "V'haarev nah..." - "and you should please sweeten for us the words of Torah." A father did not approach his study as if it is something sweet and dilectable. It came across as a burden. As such, his children did not even want to "burden' themselves with the yoke of Torah and they strayed from morality into the cardinal sins.
This approach very much simulates the famous statement attributed to Rabbi Moshe Feinstein, ZT"L that the reason so many youth did not remain religious in the early part of the 20th century because they grew up in an atmosphere where the father would constantly sigh and say, "Oy, s'iz shvihr tzu zein ah yid". (Oh, it is difficult to be a Jew).
This is the most "original" explanation.
HaRav Weiss told a story concerning Rabbi Yonasan Eibeschitz, ZT"L. The story goes that one of the congregants at Rav Yonasan's shul was fortunate to have his seat very close to the Rav and he could hear the Rav pray. This congregant was puzzled when he noticed that when R' Yonasan would say the Birchos HaShachar he would seem to omit the bracha of "Shelo Asani Goy". He couldn't fathom that this is so, so he strained himself to listen closer to the Rav. Sure enough, he had no doubt that the Rav was omitting the bracha of "Shelo Asani Goy".
The congregant was stupified. How could this be? Such an omission certainly borders on the heretical (and there was much controversy going on at the time). Not knowing what to do, he went to the city Bet Din and reported his discovery. The Bet Din took upon themselves to investigate the matter and so they summoned the Rav and asked him if this is indeed the case and what is the explanation for it?
The Rav replied that the congregant had indeed heard correctly. But he went on to explain as follows: When i wake up every morning and understand that I am fortunate to be a servant of G-d and that G-d gave me the opportunity to be a leader of his chosen people I am totally overwhelmed with the enormity of this situation. As such, I cannot hold back a single moment and as soon as my hands are clean, I pronounce the bracha of "Shelo Asani Goy". I simply cannot hold out until I arrive in shul to make this bracha and so I say it ahead of time. For this reason, I must omit it when I later say the other brachos in order.
Rav Weiss went on to say that there are 2 brachos that we hold to be m'd'oraita - Birchas HaMazon and Birchas HaTorah. But there is a clear distinction - Birchas HaMazon is said after one eats, whereas Birchas HaTorah is said prior to the Torah study. How do we explain this inconsistency?
The Rav said that when we eat, we are primarily servicing our physical needs. There is no direct spiritual benefit to eating. that being the case, it is sufficient for us to thank Hashem after we have already felt the earthly pleasure of eating. Before we eat, we cannot yet fully appreciate the benfits of the food. Conversely, when it comes to Torah learning, the spiritual pleasure should be such that we are tremendously excited over the mere fact that we are commanded to study Torah. Our zest for study should be such that we simply cannot wait to say the bracha - just like Rav Yonasan could not wait to say "Shelo Asani Goy". This is the proper approach to Birchas HaTorah. As such, Rav Yehuda in the gemara is telling us that the complaint is not that we neglected to say the bracha, but that we were not enthused to jump ahead and say the bracha spontaneously out of sheer joy - "Shelo barchu al HaTorah t'chila" we didn't feel the irrepresible urge to make the bracha in advance. This lack of enthusiasm was our downfall.
HaRav Weiss concluded the shiur by saying that even though it is prohibited to study Torah on Tisha B'Av, we must never lose sight of the fact the "Al mah avdah Ha'aretz? - Shelo birchu b'Torah t'chila!".