Acquiring Torah 38: Derech Eitz haChaim IV:
Accordingly, we see that despite the infinity not only of the Torah but even of each of its letters, it is necessary to inflame it so that it flares up. Human intellect has been similarly fashioned so that its power of comprehension is great only when it glows with the power of thought. Concerning this it is written, “The Lord grants wisdom, from His mouth come knowledge and understanding (Proverbs 2:6),” for all that exist were made by the speech of the Holy One, Blessed is He, as it is written, “By the word of the Lord the heavens were made (Psalms 33:6).”
His mouth is the root of all things created and also that which sustains them, and the breath of His mouth is the influence extending to all things created from the Source that brought them forth. Accordingly it was said, “For not on bread alone does man live, but on all that goes forth from the Lord’s mouth man lives (Devarim 8:3).” This is the breath that goes forth and sustains, and it is clothed in edible things required by man for nourishment. (Ramchal: Derech Eitz haChaim IV)
Rav Chaim Vital explains that the only reason that we are nourished by bread is because God decreed that it do so. Anyone who recognizes that food nourishes us only through the word of God will be able to study Torah and receive the highest level of Spiritual sustenance.