And the three mighty men brake through the host of the Philistines, and drew water out of the well of Bethlehem, that was by the gate, and took it, and brought it to David: nevertheless he would not drink thereof, but poured it out unto the LORD. Poured it out unto the Lord - To make libations, both of water and wine, was a frequent custom among the heathens. We have an almost similar account in Arrian's Life of Alexander: "When his army was greatly oppressed with heat and thirst, a soldier brought him a cup of water; he ordered it to be carried back, saying, I cannot bear to drink alone while so many are in want, and this cup is too small to be divided among the whole." Tunc poculo pleno sicut oblatum est reddito: Non solus, inquit, bibere sustineo, nec tam exiguum dividere omnibus possum. - Arrian, lib. vi.
The example was noble in both cases, but David added piety to bravery; he poured it out unto the Lord.