The mishna towards the end of Masechet Taanit lists five events that occurred to our ancestors on the 17th of Tammuz and five events that occurred on the 9th of Av.
Events #2-5 for each of the two days that frame the Three Weeks have something directly to do with the Churban, with the destruction of the Batei Mikdash. The first event of each day, on the other hand, occurred much earlier in our history. Theyoccurred during the infancy of the Jewish Nation, soon after we came out of Egypt. We refer to the Sin of the Golden Calf (17 Tammuz 2448) and the Sin of the Spies (9 Av 2449).
These two MAJOR sins of the generation of the Midbar, are not merely sins. They are prototypes and significant examples of the kind of sins that attack the core, the foundation of Judaism. Way back at the Burning Bush, G-d's first communication with Moshe Rabeinu, G-d told Moshe that He had heard the cries of the people in Egypt and that He 'remembers' the promises to our Avot, and that He will go down to save the people from the hand of Mitzrayim and that He will take us up from that land to a good and expansive land, a land flowing with milk and honey… He further indicated that on the way out of Egypt, en route to Eretz Yisrael, the people would serve Him on this very same mountain (Har Sinai).
G-d said it then, and shortly there- after to all the people through the Prophet Moshe, that we were being taken out of Egypt, freed, saved… and that we would make a mutual commitment with G-d and that we would be brought to Eretz Yisrael. That was the Plan. That always has been the Plan.
Torah and Eretz Yisrael. The Jewish People as a nation and each individual Jew are committed by virtue of being Jewish, to be faithful to the Torah and to Eretz Yisrael. The Sin of the Golden Calf represents turning away from G-d and His Torah. It was a betrayal of our commitment at Sinai. And even though only 3000 men were killed because of Eigel HaZahav – approx. a tenth of a percent of the total population, the other 99.9% of the nation then, and in some ways, all Jews since, bear some of the responsibility for that sin. That is, those Jews who – in any given generation – turn their back on G-d. Golden Calves come in all kinds of shapes and sizes, but there is a common factor that continues throughout the generations.
This what we mourn on 17 Tammuz. This is a root cause of our being exiled from the Land. And this is our focus to thought and action. Every effort to bring Jews closer to Torah and Mitzvot, rids us more and more of the burden of the Golden Calf that hangs over us. And the Sin of the Spies represents our turning away from Eretz Yisrael. Let's choose new leaders to bring us back to Egypt is the clarion call – again, in all different shapes and sizes, of the Meraglim. Kalev and Yehoshua exhorted the people to ALOH NAALEH. We have the weight of the Sin of the Spies on our shoulders, too.
Every effort we make to live in Israel and to encourage others to do so, brings us more in line with Kalev and Yehoshua, more in line with what G-d says repeatedly in the Torah, that the purpose of Torah and Mitzvot is to come and live a life of Torah in Eretz Yisrael. Our task and challenge is year round. The Three Weeks puts that challenge into sharp focus.