“With the heart a person believes” (Ro 10:10) which is the “inner man” (Eph 3:16). Man is composed of “spirit and soul and body” (1Th 5:23). “The Lord God formed man of dust from the ground” (Ge 2:7) which is the body. The brain is a physical organ and we make decisions with our intellect. But you “believe in your heart” (Ro 10:9) which is from another capacity. That source is from when God “breathed into his nostrils the breath of life; and man became a living being” (Ge 2:7). Job said the “‘Spirit of God has made me, and the breath of the Almighty gives me life'” (Job 33:4). You could limit God’s creation if you only considered Solomon saying “they all have the same breath” (Ecc 3:19) or Isaiah stating, “Stop regarding man, whose breath of life is in his nostrils” (Isa 2:22). But a distinction is made by Solomon saying, “Who knows that the breath of man ascends upward and the breath of the beast descends downward to the earth?” (Ecc 3:22). He says “man goes to his eternal home” (12:5) and “the dust will return to the earth as it was, and the spirit will return to God who gave it” (:7). Zechariah states that it is the Lord who “forms the spirit of man within him” (Zec 12:1). He is the “Father of spirits” (Heb 12:9). Moses referred to the Lord as “the God of the spirits of all flesh” (Num 27:16). Jesus “became a life-giving spirit” (1Co 15:45) and “breathed on them and said to them, ‘Receive the Holy Spirit'” (Jn 20:22). Therefore be careful of an “unbelieving heart that falls away from the living God” (Heb 3:12).