1 Samuel 17:38-39 (KJV)
And Saul armed David with his armour, and he put an helmet of brass upon his head; also, he armed him with a coat of mail. 39 And David girded his sword upon his armour, and he assayed to go; for he had not proved it. And David said unto Saul, I cannot go with these; for I have not proved them. And David put them off him."
In this passage, we are right in the middle of the account of Goliath challenging the Israelites to a one-on-one duel, but up to this point, no one is willing to accept. Young David shows up on the scene, and unlike his older counterparts, he is willing to accept Goliath's challenge. David sees this unruly challenge as a disrespectful and dishonorable challenge against the Israelites and God. King Saul was reluctant at first to let David go, but he has now decided to agree to the youngster's eagerness. Keep in mind that Goliath is a 9-foot-tall behemoth of a man, and David is just a small teenager; nonetheless, David is not intimidated by this giant. Saul tries to arm and protect David, so he gives him his sword and his armor. A notable fact is that Saul was a tall man himself; he was no Goliath, but taller than most men and had a noticeably larger frame than David. Maybe Saul was genuinely trying to protect David, or perhaps he thought that if he wore the king's armor, it would intimidate Goliath.
Here's the thing we need to see and learn from this passage: as we look back at the two verses, we see that David tried on all this armor and then he took it off. Why is that? David knew that God was calling him to this battle, and he also knew he had to enter that battle in the way God wanted him to. Sure, the idea of armor and a big sword seems like the right things to have in a fight such as this. But David chose to trust in God's protection rather than in others. Here is our key takeaway: God calls you to serve Him in various ways, ranging from simple tasks to what may seem like a daunting job. But we must do it God's way! Not how the world says we should, not how we want to do it, or by any other ideas or suggestions. If God leads you to a mission, He will also guide you on how to accomplish it and provide you with the resources to do it His way!