Congregation Beth Elohim, the largest and most active Reform Jewish congregation in Brooklyn, prints a lovely, succinct answer to this question on the welcome pamphlets handed to all its bar bat mitzvah guests. We reprint it here: What Everyone Should Know About Bar and Bat Mitzvah
Bar and Bat Mitzvah means that a thirteen-year-old Jewish child is old enough to perform mitzvot, the commandments of Jewish life. It is one of the most venerable and potent Jewish rituals. When a Jewish child becomes Bar or Bat Mitzvah, he or she publicly reads a portion from the Torah, the Five Books of Moses. Each week, every congregation in the Jewish world reads from the same Torah portion. In this way, Jewish youth are linked to the entire Jewish people, regardless of where the thirteen-year-old happens to live. The youth also reads a Haftarah, which is a selection from the weekly section of the prophetic writings - from Isaiah, Amos, Hosea, etc. or from historical books like Joshua, Judges, Samuel or Kings.
The Torah symbolizes the moment when God met the Jewish people at Sinai and made a covenant with them. It reminds us of God's revelation and of God's intervention in human history.
The Torah also symbolizes all that the Jewish people hold sacred: stories, laws, histories, poetry. When a Jewish child reads from the Torah, he or she is enveloped in its heritage, in its poetry, in the majesty of Sinai. He or she says to the community: "I am now an adult. I am now ready to fulfill the covenant with God by being responsible for performing mitzvot, the obligations of Jewish life."
Bar Mitzvah and Bat Mitzvah symbolize a child's entry into the adult Jewish community, a way for the entire community to say that the youngster is no longer a child, and "all we cherish, all we hope to be, the sum total of our visions, we place them in your hands. May God make you ready. May God make you strong."
