David was used by God to kill the giant Goliath because of his availability, but also because he was an expert at using a slingshot.
How many times have you and I heard someone say, "God is more interested in you being available then He is in your ability?" That is not necessarily true! Sure, God can't use us if we are not available but He has also given us strengths and spiritual gifts for a reason. When God asks his people to do something He desires it to be done well.
Let's don't play down the abilities and unique gifts God has bestowed upon us in the name of using religious sounding phrases. This begs an interesting question. "Would David had slain Goliath because he was available but did not know how to use a slingshot?" Now, of course, God could have used him in some other way. However, I take the position that God put it in David's heart to perform this feat because his heart was as mad as mad could be due to someone defying his God, and because God knew that David could get the job done.
God knows our abilities and gifts and wants to give us apportunities to use them. Of course, He can also use our weaknesses, but it is not being full of pride to step forward in confidence and take charge of a situation for the glory of God. That is what David did, and God was not the least bit offended. In fact, I can see God applauding in heaven!
If you have a desire to do something that God has put on your heart to do but you are not very good at, do it. God will still use you. He wants us to get out of our comfort zone and trust Him. However, don't shy away from using your strengths because you think it is more spiritual to depend upon God to use your weaknesses.
Be a David. Have righteous anger at circumstances that are seeking to defy God. Be avilable. Know your strengths. Step up and take charge to the glory of God.