When the will of God becomes our word for life
If, by any will of God -- that is, any truth in him -- we live, we live by it tenfold when that will has become a word to us. When we receive it, his will becomes our will, and so we live by God. But the word of God once understood, a man must live by the faith of what God is, and not by his own feelings even in regard to God. It is the Truth itself, that which God is, known by what goeth out of his mouth, that man lives by. And when he can no longer feel the truth, he shall not therefore die.
He lives because God is true; and he is able to know that he lives because he knows, having once understood the word, that God is truth. He believes in the God of former vision, lives by that word therefore, when all is dark and there is no vision.
George MacDonald, "The Temptation in the Wilderness," Unspoken Sermons Series One.