1 Samuel 14:9-10. "[I]f they say to us, 'Wait until we come to you,' then we will stand still in our place, and we will not go up to them. But if they say, 'Come up to us,' then we will go up; for the Lord has given them into our hand. And this shall be a sign to us." Jonathan is speaking to his armor-bearer who is about to accompany him into the enemy camp. Jonathan just explained that he intends to sneak away from the Israeli encampment, and go into the Philistine camp, showing themselves to the enemy. If they are told to come up to the Philistines, that will be a sign from God that He has delivered the opposing army into their hands. (Spoiler alert: the Philistines do mockingly tell Jonathan and his armor-bearer to come forward, and the two men kill about twenty of the Philistines in the night, creating a very great panic in the rest of the camp. (1 Samuel 14:13-15).)
 

Since Jonathan surely knew it is inappropriate to test God, or to establish our own rules for God to follow, this mission and "sign from God" must have been inspired by God. In some way, Jonathan must have received a message from God, maybe in a dream or during prayer. Messages like this are often difficult to follow. We second guess ourselves; we wonder if it was just our imagination, our own ego, or maybe even the devil leading us into a trap. In Jonathan's case, the risk was substantial, as he was being called to go into an enemy camp with only himself and his armor bearer.

Perhaps the armor bearer's response helped Jonathan to be sure the prompting was from God. When Jonathan explained what he intended to do, saying "[I]t may be that the Lord will work for us; for nothing can hinder the Lord from saving by many or by few" (1 Samuel 14:6), his armor bearer replied "Do all that your mind inclines to; behold, I am with you, as is your mind so is mine." (1 Samuel 14:7) So Jonathan got corroboration of God's message through the willingness of his armor-bearer to go with him.

I think God does this for us. When we commit to trying to do His will, He gives us the supplemental guidance and support we need to understand what He is asking of us and to do it. This increases our confidence in Him, and helps us channel His power, which is always the true force behind everything we do in His name.