Tisha Be'av is the ancient national day of mourning for the Jewish people. Many disastrous events have afflicted us on this ominous day. We commemorate the date of the destruction of the First and Second Temples, the latter of which began the Jewish people's long traverse into an exile, dispersal and suffering that has lasted for almost 2,000 years. During those times, Tisha Be'av became synonymous with expulsions and massacres, and was even the date that saw the beginning of the deportations from the Warsaw Ghetto to Treblinka. TISHA BE'AV must not be just a lesson in remembrance and sorrow, but should also be a day of reflection. We learn from our sages that the Second Temple was destroyed because of one reason: baseless hatred. We know that there were many righteous, learned and God-fearing Jews in the Second Temple period, but many had a view of the world which led them to look unkindly on their fellow Jews. By contrast, the First Temple was destroyed for three reasons; immorality, widespread murder and idolatry. These are extremely grave sins according to Jewish law. Nonetheless, the first exile lasted for only 70 years whereas the second has lasted for almost 2,000 years. Why the discrepancy? Rabbi Avraham Yitzhak Hakohen Kook, of blessed memory, had much to teach on this very point. He explained that the only punishment worthy of baseless hatred is the destruction of our national center. This means that the Jewish people needed to experience a long hard exile that broke down our established, mistaken frameworks. These frameworks were the source of the division, and Kook asserted that while they existed, the misdeeds, mischaracterizations, baseless hatred and, indeed, the exile these brought, would continue. After 2,000 years we have finally returned to our ancestral home but we are still suffering from severe divisions among our people, both open and hidden. The State of Israel faces many challenges that we can only overcome as a united people. We are presented with a growing nuclear threat from Iran, terrorist groups primed to strike once again into our city centers, rockets aimed at our towns and villages in the North and South, and the increasing hatred and delegitimization of Israel around the world. TODAY, THE State of Israel is a thriving pluralist and multicultural society. However, recently we can see major strains of disunity of purpose, and discord. Many see the different elements in Israeli society as the "other" and frequently defame them. Many groups pull their weight as citizens for the good of the country, while others contribute far less. We need to achieve a national solidarity which pulls in the same direction to meet the rising challenges which we face as a nation. It can surely only contribute to disunity when Israelis of some religions and backgrounds send their children to the front lines in the battles against our enemies and those who seek to destroy us, while others do not. We understand that for religious, ethnic or cultural reasons, many groups feel they cannot contribute fully to the physical defense of our nation. However, there can surely be contributions made in other ways, either through national or communal service. Every community has its sick, its disabled, its aged and its poor. We call on every Israeli to contribute to the betterment of our society and in this drive become unified for a central purpose. In a free society like Israel's, every person is entitled to their own opinion. Nevertheless, this does not include inciting violence or hatred for other groups, and especially not for Israel as a whole. Such incitement will essentially lead to the breakdown of our vital national solidarity and weaken our resistance to those who seek the destruction of every one of us. Regaining our national home was achieved only by standing together. I have heard many amazing stories about the War of Independence in which people from many religions, backgrounds, nationalities and cultures stood side by side on the ramparts to fight for our country. While we retained the right to our differences, we remembered that we were all striving for the same goals. Now is that time once again. Our sages and our bitter experiences have taught us that the gravest sin of all is human pride, with its baseless hatred and disunity of purpose, and for that we received the gravest punishment. We cannot allow ourselves to lose sight of what is important even while retaining our right to be and to think differently. This must be the lesson of Tisha Be'av for us all. The writer is deputy minister of foreign affairs.