Now faith is the assurance of things hoped for, the conviction of things not seen. For by it the people of old received their commendation. By faith we understand that the universe was created by the word of God, so that what is seen was not made out of things that are visible. (Hebrews 11:1, ESV).
There are many definitions of faith. "Faith" is perhaps a unique word, a word that is not intended ever to be fully understood, but experienced and lived and learned until the final moment of life.
Our atheist friends probably find ways to trivialize this word, but we know it to be the thing that saves us. It is our source of joy when first we begin to understand the good news of Jesus Christ; that our sins are forgiven and our salvation is assured through the death and resurrection of our Saviour. At some point we will realize that our faith is no mere act of will, but a gift from God, enabled through Christ and received by the Spirit.
When someone is suffering from serious illness, it is no time to be shy. If they have not yet heard or understood the good news, it is time they did. It is time they heard it from a friend, in a kind, gentle and confident way.
Then there is the case of our Christian friends who might be suffering. We might normally consider them to be very mature Christians, but because of ill health, agonizing pain or personal loss they almost appear to have lost their faith. What shall we say to them?
In some cases perhaps little needs to be said. Our presence, our friendship, our love may be the best we can do. Very few people, in the throes of pain, are likely to cry out "I need to hear a good speech."
In other cases there may be an earnest and thoughtful questioning of the ways of God. We need to listen very carefully. With God's help, we can try to respond. In a response written with atheists in mind, David J. Wolpe writes:
Why does faith matter? Love of this world, of one another, is the sole hope in an age when we can destroy the world many times over. There is no power that is only good, that cannot be twisted for evil. Religion is hardly an exception. But while there are many things that can doom us, there is only one thing that can save us. Faith. Not blind or bigoted faith, but faith that pushes us to be better, to give more of ourselves, to see glimmers of transcendence scattered throughout our lives. Such faith is both an achievement and a gift: it is an achievement of seeking, questioning, yearning, reasoning, hoping, and it is a gift of God, who fashioned this world, whose goodness sustains it and whose teachings could save it if only we-believers and deniers both-would listen, would love.
However problematic faith might seem at times, the absence of faith is even more baffling to the human spirit. With faith, wonderful possibilities open up, both here and now and for eternity.
As for our friend in extreme pain, he may not want to listen to us-just as we might feel if we were in his position. But we can pray for him, pray that he will hear a voice within his soul, saying with power and with comfort: "Be still, and know that I am God." (Psalm 46:10).
In faith and fellowship,
 David J. Wolpe, Why Faith Matters (New York: HarperCollins), 2008, pp. 197-198.