Buddhism is a religion based on rationality, objectivity, personal experience, and practice. It does not say anything about God. In fact, whether a person believes in any divine power at all is immaterial to Buddhism. What does matter? The mind. Delusions of the mind are what Buddhism seeks to eliminate. Opening and purifying the mind is its process, and freedom of the mind—nirvana—is its ultimate goal.
The term "nirvana," the way Buddhists use it, is not the same as the idea of heaven. Nirvana is the state of liberation from the dictates of the senses. While the Buddha said, "Bliss is nirvana," this absolutely does not mean a dreamy, insensible state—indeed, the closer to nirvana one becomes, the more fully present and aware they are. Truth cannot be sought or expected anywhere but here.
Buddhism is also a faith of great compassion. The Buddha himself was a man of enormous compassion, not judging others by appearance or caste, welcoming women and outcasts as students and training them as teachers, and ministering to those less fortunate with his own hands. The Buddha's strength in both head and heart has allowed Buddhists through the ages to choose a path to follow that speaks best to them, and major divisions of Buddhism have formed as a result—some focused on the mind, others on the heart. Happily, and instructively, the constant emphasis in Buddhism on being at peace within oneself and with other people has meant that these spiritual divisions have not resulted in significant conflict among their followers, contrasting sharply with what we will see later in Islam and Christianity.
The Buddha grew up in the Hindu society of India, and he believed in reincarnation. However, he did not believe in a physical soul that transmigrated to the next body. Rather, he likened a person's selfhood to a wave in the sea: As a wave moves along, its substance changes completely and constantly, but we can still recognize it as the same wave. The Buddha believed that a person's essence was like the wave, completely changing physical form but continuing on its path. He taught that achieving nirvana or full awareness could release someone from having to return in a physical body.
According to Buddhist philosophy, the only constant in the universe is change itself—impermanence. The Buddha said:
Life is a journey; death is a return to earth.
The universe is an inn; the passing years are like dust.
Another Buddhist phrase, "This too shall pass," has become popularized in recent years, and is a succinct statement of this fundamental Buddhist tenet.