This past week in my message from Luke 9.37-45 I made a few statements about how not believing God's word is essentially calling him a liar, and so then, not believing God as he has revealed himself through his word is a sin. I still stand on by those statements, based upon 1 John 5.10: "Whoever believes in the Son of God has the testimony in himself. Whoever does not believe God has made him a liar, because he has not believed in the testimony that God has borne concerning his Son." I've been thinking about this for the past few days, and I believe there are a few important distinctions that need to be made.
I recently read this article by Chuck Swindoll, in which he does not fault the father of the demon-possessed boy for his unbelief. Swindoll goes on to tell about how he preached at his own father's funeral, and gave his family the hope of the resurrection, and several other biblical encouragements. He was later confronted by his sister, who asked him if he really believed all of the things that he said at his father's funeral, to which Swindoll replied something to the effect of, "No, I guess not. I can't really wrap my mind around a lot of those things." Swindoll then goes on to say how it's liberating to not know everything, and that Christians must be careful about having all the answers when in fact they really don't, all of which I agree with.
There is, I believe however, a difference between faith and understanding. The two are not necessarily linked. For example, I don't understand the mystery of the incarnation. I can't wrap my mind around how the infinite became finite. I don't understand how the invisible became visible. But, just because I don't understand it, it doesn't mean I don't believe it. Another good example would be the act of creation: I can't comprehend the kind of power it takes to create with a word, but I believe that it happened. Or take the Trinity: three equal persons, yet one. It doesn't make sense, but I believe it. In other words, you don't necessarily have to understand in order to believe.
There is a difference between those things and the lapses of faith evidenced by the father of the demon-possessed boy and the disciples in Luke 9.37-45. Those folks KNEW what Jesus was capable of and saw it with their own eyes, and still did not believe. There is biblical evidence to support the fact that the father of the boy was actually a regular follower of Jesus, and yet he approaches him by saying, "If you can...." The disciples were specifically given power over all demons, and yet they cannot cast this one out.
In this sense, it would be sin for me to know about the mystery of the incarnation, and NOT believe it, even if I can't understand it. Why? Because scripture makes it pretty clear: God became a man who was the same in every way to all other men except that he did not sin. To not believe that is sin because it is what scripture testifies to.
So then, in conclusion, we shouldn't be concerned about sinning because we can't understand something; there are limits to our powers of reason and understanding. But even if we do not understand, we must still believe.