01. The Law
Goliath had size and armor. David had a Name. "You come with a sword... I come in the name of the LORD." David trusted his representation, not his aim.
"You come to me with a sword and with a spear and with a javelin, but I come to you in the name of the LORD of hosts."
02. The Mechanics
The mechanic is Spiritual Superiority. The battle was spiritual. Invoking the Name brings Heaven's Army. The giant fell because he defied the wrong Authority.
03. The Application
Facing a giant? Don't compare your size to his; compare his to God. Go "in the Name". Authority is about Who is with you. The stone is just the contact point for God's power.