The reality of man is his thought, not his material body. The thought force and the animal force are partners. Although man is part of the animal creation, he possesses a power of thought superior to all other created beings. – Abdu’l-Baha, Paris Talks, pp. 17-18.

Why not material body?

In Europe I told the philosophers and scientists of materialism that the criterion of the senses is not reliable. For instance, consider a mirror and the images reflected in it. These images have no actual corporeal existence. Yet if you had never seen a mirror, you would firmly insist and believe that they were real. The eye sees a mirage upon the desert as a lake of water, but there is no reality in it. As we stand upon the deck of a steamer, the shore appears to be moving, yet we know the land is stationary and we are moving. The earth was believed to be fixed and the sun revolving about it, but although this appears to be so, the reverse is now known to be true. A whirling torch makes a circle of fire appear before the eye, yet we realize there is but one point of light. We behold a shadow moving upon the ground, but it has no material existence, no substance … In brief, the senses are continually deceived, and we are unable to separate that which is reality from that which is not. – Abdu’l-Baha, The Promulgation of Universal Peace, p. 21.

How about the Human Brain or intelligence  

Like the animal, man possesses the faculties of the senses, is subject to heat, cold, hunger, thirst, etc.; unlike the animal, man has a rational soul, the human intelligence. This intelligence of man is the intermediary between his body and his spirit. – Abdu’l-Baha, Paris Talks, p. 96.

If a man’s thought is constantly aspiring towards heavenly subjects then does he become saintly: if on the other hand his thought does not soar, but is directed downwards to centre itself upon the things of this world, he grows more and more material until he arrives at a state little better than that of a mere animal. – Ibid., pp. 17-18

How to Grow Your Soul:
https://bahaiteachings.org/divine-common-sense-grow-soul?utm_source=BT+Subscribers&utm_campaign=16902785b2-RSS_EMAIL_CAMPAIGN_NEW&utm_medium=email&utm_term=0_22fe645b0d-16902785b2-114045481&mc_cid=16902785b2&mc_eid=a5e50159ab

How can one increase in faith?  You must strive. A child does not know, in learning he obtains knowledge. Search for Truth.

There are three kinds of Faith: 

first, that which is from tradition and birth. For example: a child is born of Muhammadan parents, he is a Muhammadan. This faith is weak traditional faith: 

second, that which comes from Knowledge, and is the faith of understanding. This is good,

but there is a better, the faith of practice. This is real faith.

We hear there is an invention, we believe it is good; then we come and see it. We hear that there is wealth, we see it; we work hard for it, and become rich ourselves and so help others. We know and we see the Light, we go close to it, are warmed by it, and reflect its rays on others; this is real faith, and thus we receive power to become the eternal sons of God. 

– Abdu’l-Baha in London, pp. 64

The light of a good character surpasseth the light of the sun and the radiance thereof. Whoso attaineth unto it is accounted as a jewel among men. The glory and the upliftment of the world must needs depend upon it. – Tablets of Baha’u’llah, p. 36.