Humanity’s natural condition, since the fall of Adam and Eve, is characterized by unbelief. As Paul says in Romans 1:18–3:20, we do not trust the God who is revealed in nature, and we deny His sovereign right to rule over us. The result is enslavement to wickedness. Belief, or faith, determines whether one has been rescued from sin and misery (Eph. 2:8–10). By faith alone we move from being enemies of God to being His children.
The faith of which we speak—saving faith—is not equivalent to knowledge, though it includes knowledge of the One in whom faith is placed. We see this in Mark 9:20, when the demon-possessed boy is brought to Jesus. Upon seeing the Lord, the demon reacts violently, throwing the boy to the ground. Clearly, the evil spirit knows that it is in the presence of the Almighty, but it does not trust in Him. Knowing God’s rightful rule, the demon nevertheless rejects it and displays open rebellion toward the Son of God.
On the other hand, the father of the demon-possessed young man illustrates true faith. When given the opportunity to trust Christ, the boy’s father says that he believes Jesus can help his son (vv. 21–24). But the faith that the man has is not a perfect faith, for at the same time he says that he believes Christ, he also exclaims, “Help my unbelief!” In other words, the faith the father possesses is true, albeit weak, and we know this to be the case because Mark 9:25 indicates that Jesus acts according to the man’s faith-motivated request—He heals the man’s son. In all this, we learn an important lesson, namely, that the efficacy and power of faith is found not in the strength of the faith but in the strength of faith’s object. Even the weakest trust in Christ is enough, for what is necessary to receive Him and all His benefits is true faith, not perfect faith.
That being said, we dare not rest content with a weak faith. Instead, we are called to partake of God’s means of grace to strengthen our faith and “go on to maturity” (Heb. 6:1). John Calvin comments on today’s passage: “As our faith is never perfect, it follows that we are partly unbelievers; but God forgives us, and exercises such forbearance towards us, as to reckon us believers on account of a small portion of faith. It is our duty, in the meantime, carefully to shake off the remains of in delity which adhere to us, to strive against them, and to pray to God to correct them, and, as often as we are engaged in this conflict, to fly to him for aid.”