"He must purge his breast ..."

"But, O my brother, when a true seeker determineth to take the step of search in the path leading to the knowledge of the Ancient of Days, he must, before all else, cleanse and purify his heart, which is the seat of the revelation of the inner mysteries of God, from the obscuring dust of all acquired knowledge, and the allusions of the embodiments of satanic fancy. He must purge his breast, which is the sanctuary of the abiding love of the Beloved, of every defilement, and sanctify his soul from all that pertaineth to water and clay, from all shadowy and ephemeral attachments. He must so cleanse his heart that no remnant of either love or hate may linger therein, lest that love blindly incline him to error, or that hate repel him away from the truth. Even as thou dost witness in this day how most of the people, because of such love and hate, are bereft of the immortal Face, have strayed far from the Embodiments of the divine mysteries, and, shepherdless, are roaming through the wilderness of oblivion and error. That seeker must at all times put his trust in God, must renounce the peoples of the earth, detach himself from the world of dust, and cleave unto Him Who is the Lord of Lords. He must never seek to exalt himself above any one, must wash away from the tablet of his heart every trace of pride and vainglory, must cling unto patience and resignation, observe silence, and refrain from idle talk. For the tongue is a smouldering fire, and excess of speech a deadly poison. Material fire consumeth the body, whereas the fire of the tongue devoureth both heart and soul. The force of the former lasteth but for a time, whilst the effects of the latter endure a century."

-Bahá'u'lláh, The Kitáb-i-Íqán, pp. 192-193