Man experiences a time when both the heart and mind do not possess any faculties or powers at all. Then a time comes when the brain begins to grow and develop. Then a stage arrives when the faculties and powers of the heart are developed, after which the heart becomes enlightened, ignited and illuminated. When the heart arrives at this point, a human being reaches the stage of spiritual maturity, and the brain becomes subservient to the heart, and the faculties of the mind no longer control the qualities and faculties of the heart.
It should also be remembered that these various states of the mind are not specific to believers alone. Hindus and people from among the scheduled classes all make use of the brain. Moreover, those who are engaged in worldly affairs and business, all make use of their brains. The mental faculties of such people have grown and developed fully, and it is through these faculties that they come up with new and innovative ideas to further their business. Look at Europe and the New World, and you will see how its people make use of their mental faculties, and the pace at which they invent new technologies. The work of the heart begins when a person becomes devoted to God. At such a time, all the inner faculties and authorities of man cease to exist and the rule of the heart gains a power and strength. It is then that a human being may be deemed complete.
Hazrat Mirza Ghulam Ahmad (as), Malfuzat – Volume II (Farnham, Surrey: Islam International Publications Ltd., 2019), 120-121.