The tenth day of Teves is a fast day, on which we remember the beginning of the siege of Jerusalem that led to the destruction of the Temple. By depriving ourselves of food and drink, we experience the discomfort of hunger and thirst, and in this way we share in the national distress.
No other nation has anything similar to a fast day for an event that occurred thousands of years ago. Most historic events are remembered by historians interested in the subject. The average person is untouched by such ancient events.
Not so with Jews, for whom spirituality and closeness to God are a vital part of life. The loss of intimacy with God that occurred with the destruction of the Temple is something from which we have never recovered, and is a source of grief today. The fast of the tenth day of Teves is not merely a commemoration of a historic event, but an expression of the grief we experience today in being deprived of the close presence of God in the Temple.
We have been promised that the Temple will be restored with the ultimate Redemption of Israel, and we will again have the Shechinah which is the breath of spiritual life. To achieve this Redemption we must merit it, by committing ourselves to total observance of Torah and mitzvos.