We need our daily substance. Square meals, a roof over our heads. We need our daily bread to survive.
But is this stuff the true substance of life?
The New Testament defines faith as: “the substance of things hoped for.” (Hebrews 11:1)
In the books of the gospels, we read many sayings of Christ. He teaches many things, gives commands and advice. But above all, He makes promises. The Beatitudes are often called Christ’s Law, the Law of the New Covenant. They are promises, promises of blessedness for those who follow Him. We believe His promises. We live for the fulfillment of His promises.
In his encyclical letter on hope which he gave us a year ago, Pope Benedict considered the question of the true substance of life. In paragraphs 8-9, he explains how what we really live by is not food. We need food; we need stuff–but not as much as we need God. The martyrs gave up the material substance of life, because they knew they could not live without faith in the promises of Christ.
The substance of life is not food. It is faith.
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Father Mark White Blog 
I noticed that this is not the first time at all that you write about the topic. Why have you decided to write about it again?