Bahá’í Sacred Writings, ‘Abdu’l-Bahá, #445

As to the fundamentals of teaching the Faith: Know thou that delivering the Message can be accomplished only through goodly deeds and spiritual attributes, an utterance that is crystal clear and the happiness reflected from the face of that one who is expounding the Teachings. It is essential that the deeds of the teacher should attest the truth of his words. Such is the state of whoso doth spread abroad the sweet savours of God and the quality of him who is sincere in his faith.

Once the Lord hath enabled thee to attain this condition, be thou assured that He will inspire thee with words of truth, and will cause thee to speak through the breathings of the Holy Spirit.