Human utterance: “its influence and…moderation” when teaching the Cause of God

Teach thou the Cause of God with an utterance which will cause the bushes to be enkindled, and the call 'Verily, there is no God but Me, the Almighty, the Unconstrained' to be raised therefrom. Say: Human utterance is an essence which aspireth to exert its influence and needeth moderation. As to its influence, this is conditional upon refinement which in turn is dependent upon hearts which are detached and pure. As to its moderation, this hath to be combined with tact and wisdom as prescribed in the Holy Scriptures and Tablets.... 

- Baha’u’llah  (‘Tablets of Bahá'u'lláh Revealed after the Kitab-i-Aqdas’; The Compilation of Compilations, Vol. II, Guidelines for Teaching)