How we can increase our “ability and capacity”

During thy supplications to God and thy reciting, “Thy Name is my healing," consider how thine heart is cheered, thy soul delighted by the spirit of the love of God, and thy mind attracted to the Kingdom of God! By these attractions one's ability and capacity increase. When the vessel is enlarged the water increases, and when the thirst grows the bounty of the cloud becomes agreeable to the taste of man. This is the mystery of supplication and the wisdom of stating one's wants. (‘Abdu’l-Baha, quoted by J.E. Esslemont in ‘Bahá'u'lláh and the New Era’; The Compilation of Compilations, Vol. II, The Importance of Prayer, Meditation and the Devotional Attitude)