Bodily Postures in Worship

“The inward attitude certainly holds first place in prayer, but outward signs, kneeling, uncovering the head, lifting up the hands, have a twofold use. The first is that we may employ all our members for the glory and worship of God; secondly, that we are, so to speak, jolted out of our laziness by this help. There is also a third use in solemn and public prayer, because in this way the sons of God profess their piety, and they inflame each other with reverence of God. But just as the lifting up of the hands is a symbol of confidence and longing, so in order to show our humility, we fall down on our knees.” 

John Calvin, Commentary on Acts 20:36