Entering The Heart And Brain
Translation of an excerpt from Degel Machaneh Ephraim, Parshas Ekev (via Israel613.com):
The Baal Shem Tov related that people of a certain country sent a letter to the Rambam, asking him to prove to them from the Torah that the dead will come to life. The proofs mentioned in the Gemara were not sufficient for them, since they felt that all the verses quoted by the Gemara could be explained otherwise.
The Rambam refused to reply to them, but delegated the task to his disciple, Rabbi Shmuel ibn Tibbon. The latter wrote as follows: According to science, all food and drink are converted to blood. From the blood, it goes into the liver, and from the liver, the purest goes into the heart. From the heart, the best and most refined blood enters the brain, the seat of a person's intellect and life. One who is cautious in the field of forbidden foods, is assured that his blood will be pure and clear, and he will have a pure heart. His brain will be pure enough to attain a pure spirit of life, which is the divinity of all the worlds, which keeps them all in existence. The more one watches himself and sanctifies his eating habits according to G-d's Torah, the more his intellect sanctifies all his two hundred forty-eight limbs.
Likewise, if one is lax in this respect, his intellect becomes defiled and is regarded as dead, which is the highest degree of uncleanness. Thus the holy spirit of all the worlds leaves him, leaving him vulnerable to all sorts of false doctrines and ideas. Therefore, the rabbis of the Talmud were extremely conscientious in their observance of these laws, so as not to defile themselves with food and wine of Gentiles. Consequently, their intellect was brilliant, the holy spirit of the Almighty rested upon them, to enable them and to explain every hidden meaning of the holy Torah. Since He and His Torah are one, a Divine power rested upon them and the light of their souls joined these two components to form a three stranded cord, which will never be torn.
These people, however, are surely unclean. Consequently, their blood is unclean, and their hearts and brains have become clogged by dint of the forbidden and unclean foods. They, therefore, are inclined to believe in apikorsus, denial of the Torah teachings, and have been unable to accept the sweetness and pleasantness of our Sages' words, built on their Divine intellect. Since they have become brazen and have left the faith, the destroyer will come upon them and will destroy them and theirs.
Not long afterwards, a powerful king invaded their country and put them to death, scattering all their belongings.