He wishes again to assure you he will pray for your spiritual advancement in the Holy Shrines. The power of God can entirely transmute our characters and make of us beings entirely unlike our previous selves. Through prayer and supplication, obedience to the divine laws Bahá'u'lláh has revealed, and ever-increasing service to His Faith, we can change ourselves.
(From a letter dated 22 November 1941 written on behalf of Shoghi Effendi to an individual believer; The Compilation of Compilations, Vol. II, The Importance of Prayer, Meditation and the Devotional Attitude)