" ... that this lump of coal may become a diamond and this barren tree may be grafted and yield fruit .."

"This is the wisdom of the appearance of the Prophets: to educate humanity, that this lump of coal may become a diamond and this barren tree may be grafted and yield fruit of the utmost sweetness and delicacy. And after the noblest stations in the world of humanity have been attained, further progress can be made only in the degrees of perfection, not in station, for the degrees are finite but the divine perfections are infinite."

‘Abdu’l-Bahá, Some Answered Questions