This very old symbol is found in ancient Egypt, where it is a symbol of the Ogdoad, the eight emanations of the manifested creation. Gnostics borrowed the symbol to represent the eight Aeons, and resurrection. In Christianity, the number eight is connected to the day of Christ’s resurrection, where it is referred to as the “eighth day” of the week.
The number is also repeated in biblical resurrection stories, which number eight, beginning with Elijah’s resurrection of the Widow’s son and ending with Paul’s revival of Eutychus in the Book of Acts.
The eight spoked cross in Catholicism is called the baptismal cross, and represents both the age of baptism in the church (eight days/years), and the eight day interval between Christ’s entry into Jerusalem and his resurrection. Baptismal fonts are commonly eight-sided, to carry over the symbolism of resurrection to the baptismal rite.
Today, the eight armed cross is more commonly used as a symbol for Neo-Gnosticism.