Semites, when praying, stretch out their arms and lift up their hands as though they were about to receive something. This is a gesture of supplication. When men plead before a high official of church or state, they lift up their hands, making gestures of sincere appeal. When they stand at attention, their hands are folded in front of them. When people beg for mercy they also stretch out or lift up their hands. “Lift up holy hands” means to plead with a sincere heart and motive.
(Lamsa, George. New Testament Commentary, A.J. Holman Co.,