The phrase “blessed be” is found in many modern magical traditions. Although it appears in some Pagan paths, it’s typically more likely to be used in a NeoWiccan context. It’s a traditional greeting, and to say “Blessed be” to someone indicates that you wish good and positive things upon them.
The phrase’s origins are a bit more murky. It is part of a longer ritual which is included in some Gardnerian Wiccan initiation ceremonies. During that rite, the High Priest or High Priest delivers what it known as the Five Fold Kiss, and recites,Blessed be thy feet, which have brought thee in these ways,
Blessed be thy knees, that shall kneel at the sacred altar,
Blessed be thy womb, without which we would not be,
Blessed be thy breasts, formed in beauty,
Blessed be thy lips, that shall utter the Sacred Names of the gods.
It’s important to keep in mind that Wicca is a newer religion, and many of its terms and rituals are rooted in Thelema, ceremonial magic, and hermetic mysticism. As such, it’s not surprising that many phrases – including “Blessed be” -- appear in other places long before Gerald Gardner incorporated them into his original Book of Shadows.
In fact, the King James Bible includes the verse, “Blessed be the name of the Lord.”
Like many other phrases in the Pagan lexicon, there is no universal rule that you must use “Blessed Be” as a greeting or in a ritual context. If your tradition requires it, then feel free to incorporate it – otherwise, it’s entirely up to you.