“Then David spoke to the men who were standing by him, “What will be done for the man who kills this Philistine and removes the disgrace [of his taunting] from Israel? For who is this uncircumcised Philistine that he has taunted and defied the armies of the living God?””1 SAMUEL 17:26 AMP
David was speaking from a certain perspective, he knew what God was capable of doing. He knew his God. God had delivered David from the lion and the bear. David was speaking from personal knowledge and experience. There is no changing a person or their mind when there is a real encounter. He had a relationship with God, which causes an awareness of who one is in Christ. We have certain rights as a child of God!
We can ask, declare and live in that position of authority and power. Now that's a man who knows who his God is.