Good question. I had to look it up. It appears there are several theories, but no one is completely certain of the origin. Some possibilities are: - It stemmed from Jewish tradition, predating Jesus. - When shackled, your hands are held together. Holding your hands together willingly showed an acknowledgement of another individual's power and authority. - It was a symbol of humility, similar to the stance one might take when being (which includes kneeling as well). - Placing two hands symbolized the coming together of the mortal and diving, body and soul, earth and heaven. Think of it as a western parallel to yin and yang. I realize that's not a definitive answer, but I hope it helps.