According to Dartmouth College, the number three is symbolic in "Macbeth" because it is an important number in both paganism and Christianity. Three represents the triad: father, mother and child; birth, life and death; Father, Son and Holy Spirit.
The number three has a mystical pull on both pagan and Christian beliefs. In "Macbeth," there are three witches at the very beginning of the book. According to Cedar Crest College, these three witches are symbolic of the three fates in mythology. In the play, the witches are a foreshadowing of dark things to come. Three is a particularly prominent number when it comes to witchcraft because the goddess of witches, or the Moon Goddess, has three phases. For instance, Hecate is the head witch in the play and, according to mythology, Hecate is also a goddess in Greek mythology associated with witchcraft.
Dartmouth College relates that there are famous trios throughout history and mythology. There are three gods of Babylon, which represent heaven, earth and the abyss. Egyptian mythology has three sun gods: Horus the rising sun, Ra the midday sun and Osiris the setting sun. Each represents a different phase of the sun. There are the three fates in Greek mythology, as well as three furies: Resentful, Relentless and Avenger. Their foils are three graces: Beauty, Gentleness and Friendship.