1 Samuel 21:9

And the priest said, The sword of Goliath, the Philistine, whom thou slewest in the Valley of Elah, 1 Samuel 17:2, behold, it is here wrapped in a cloth behind the ephod, deposited for safe-keeping in the national Sanctuary, as a thanksgiving offering to the Lord and as a constant reminder of His merciful help in overcoming the enemies; if thou wilt take that, take it; for there is no other save that here. And David said, There is none like that; give it me. It was valuable not only on account of its great size and good workmanship, but also on account of its associations. David may have felt that it was a holy weapon, promising him victory. He who goes forth to the battles of life with the blessing of God, with the weapons sanctified by His presence, may rest assured that no danger can really harm him.