During these three weeks we restrict celebrations and events related to happiness. In remembrance of the three weeks between the collapse of the city walls (17th of Tamuz) and the destruction of the Bet haMiqdash in Jerusalem (9th of Ab) in the year 68CE (according to Maimonides, the 17th of Tamuz commemorates the breaching of the walls of the second Bet HaMiqdash). This is why we don't celebrate weddings or we don't recite the blessing shehecheyanu, etc. during these days.
The most noticeable liturgical tradition for these three weeks is that we read special Haftarot. The Haftara is the text from the books of Prophets which is read after the weekly Tora section. The Haftarah usually relates to the content of the week's Parasha. The Haftarot during these three Shabbatot, not thematically related o the Tora portion, are known as telata depur'anuta, three Haftarot of "sorrow". They are the two opening chapters of Jeremiah and the first chapter of Isaiah.
They contain the messages of warning of the Prophets of Israel, announcing that if the Jewish people fails to follows God's commandments and worship idols and does other abominations, haShem will remove His special protection from them, and they will be on their own to face the enemy. The consequences will be destruction and exile. Because the enemy is more powerful than Israel. And cruel and merciless.
Nevertheless, each one of these Haftarot ends with a message of hope: even if temporarily Israel will fall in the hands of the enemy, God will never abandon them forever. The gates of Teshuba (repentance/reconciliation) will be always open. Israel will eventually come back to their land and God and His people will be reunited again
These Haftarot should inspire us to reflect on our own spiritual situation, to improve our own ways and follow closely HaShem's will.
HOTD WILL RESUME B'H BY THE END OF NEXT WEEK
√ For this week's Haftara click HERE
√ A good website for the Haftarot, by Reuben Ebrahimoff http://www.haftorahman.com/