God is no respecter of persons. He will use those who are willing to be used by Him, but being willing and being ready are too different things. As you have read in the scripture above, God said first to prepare. Our hearts need to be prepared for a battle. If your heart is not in it, then you will be taken out before you even get started. Whether it is a real war, or your personal battles, your heart has to be ready for what you will face.
† ♥ ✞ ♥ † If you took the love of all the best mothers and fathers who ever lived (think about that for a moment)--all the goodness, kindness, patience, fidelity, wisdom, tenderness, strength and love--and united all those virtues in one person, that person would only be a faint shadow of the love and mercy in the heart of God for all of us. † ♥ ✞ ♥ †