It is actually understood, it is not locution. Watch beat ("hit"), hand (as synecdoche by your palm), clap, and since it is published beat the palms.
Raise your hands and move them from one side to the other.
Beating the palms of the hands is synonymous with cheer. The main function of clap is to show personal approval as a sign of joy or praise for what we see or hear. He also applauded as a sign of praise, as in the Church.
It is striking the palms of the hands together