Michael Spott has a letter that I believe every one should have a look at. It is excerpted in part here but worth the read.
Dear brother, don’t be discouraged because of your seeming lack of words. Even the best orator’s speech may fall on deaf ears, but the Spirit has a voice of His own which cuts straight to the hearts of men. Have you only enough words to say, “Father, thy kingdom come,” you may trust that in response to your humble, fervent prayers the Spirit may speak many into His Kingdom. God who spoke the heavens into existence can as easily declare new creations in the hearts of unbelievers.
“In the beginning, God created the heavens and the earth. The earth was without form and void, and darkness was over the face of the deep.”
What is unbelief but a formless void, a deep darkness in man’s heart?
“And the Spirit of God was hovering over the face of the waters. And God said, “Let there be light,” and there was light.”
Was it not so with us, that inside our hearts all was dark with unbelief, when suddenly the light of faith shone and we believed? The Spirit hovered over us creating life out of nothing. Therefore trust in Jesus’ miraculous power to work through what few words you have, just as he fed many with a few fish. After all, great eloquence did not win us, but the plain and simple promise that Christ receives sinners. Faith comes by hearing, and hearing by the Word, but you see it is more important that the Spirit grants believing ears than for you and I to learn more complex ways of saying, “Trust in Christ, who lived and died in our place.” Those words are clear enough to anyone who can hear.
Brother, if your words are naturally few, perhaps it is because He intends to do more of the talking?
“Do not be anxious how you are to speak or what you are to say, for what you are to say will be given to you in that hour. For it is not you who speak, but the Spirit of your Father speaking through you.” (Matt. 10:19-20)
Had God wanted you to have more and stronger words, I believe He would have supplied you with them, but His power is magnified through weakness. Perhaps it goes for you as it did for Gideon, that God left him with fewer natural resources so that none would doubt where his victory came from. God is never limited, but limits our natural abilities to increase our faith. [continued on link below]
Excerpt from Letter to a brother who has difficulty speaking of Christ by Michael Spott