Isaiah again speaks joyfully of the Lord and the effects of his coming; all tears shall be wiped away and death shall be destroyed.
Think of what it means that death shall be destroyed. We shall never die. That is a huge promise, when all around we see people dying. But death shall be defeated when the promised one comes.
And how does Isaiah know all this? "Because the Lord has said so."
That is the reason as to why Isaiah believes all these prophesies, because the Lord has said so. Now that is the kind of faith that we are called to imitate, the faith that says "if Jesus says so then it is true." Simple as that.
"I and the Father are one!" Then it must be true. "To know me is to know the Father" also true. "No more death," the Lord says, so then there is no more death. The act of stopping to breath is only a moving on sign!