2 Samuel 23:16 So the three mighty men broke through the camp of the Philistines, drew water from the well of Bethlehem that was by the gate, and took it and brought it to David. Nevertheless he would not drink it, but poured it out to the Lord.
When the three mighty men teamed up they were able to get into the Philistine stronghold and draw fresh water from the well to bring back to their king.
They did this out of love and loyalty, being willing to sacrifice themselves for their king. But what David did must have made them wonder why they had risked everything!
David was after spiritual filling rather than fresh water. The price paid for fetching that water made it a suitable sacrifice to God, one that David did not take lightly!