And He said* to them, “Because of the littleness of your faith; for truly I say to you, if you have faith the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible to you.
Matthew 17:20 (NASB)
God cautions us to be tender to His lambs, but no one can ever be as gentle as the Father Himself. Scripture lists three ranks of saints– “fathers,” “young men,” and “little children” (1 John 2:12-14). The Spirit of God shows His concern by mentioning the young ones first and delivering the sweet promise of mercy to them: “I write to you, little children, for your sins are forgiven you for my name’s sake” (v. 12). In plain terms He says their sins are forgiven. And at the same time He stops the mouth of guilt from discouraging them and opposing the Gospel– forgiven for His name’s sake, a name far mightier than the name of a person’s worst sin.
Sincerity, then, keeps up the soul’s credit at the throne of grace so that no sin or weakness can hinder its welcome with God. Regarding iniquity in the heart, not just having it, keeps God from hearing our prayer (Psalm 66:18). This is a temptation which Christians often wrestle with when they let their personal shortcomings turn them away from prevailing prayer– they cower like some poor people who stay away from church because their clothing is not as fine as they would like.
To take care of this problem God has provided the promises– which, in any case, are our only ground for prayer– and has made them to fit the tiniest degree of grace. And as a well-done portrait faces everyone who enters the room, so the promises of the Gospel covenant smile upon everyone who sincerely looks to God in Christ. Scripture does not say, “If ye have faith like a cedar,” but “if ye have faith as a grain of mustard seed” (Matthew 17:20). Justifying faith is not beneath miracle-working faith in its own sphere. The least sincere faith in Christ removes the mountainous guilt of sin from the soul. Thus every saint is said to have “like precious faith” (2 Peter 1:1). In Genesis we can barely see Sarah’s faith, but in Hebrews 11 God gives it honorable mention, alongside Abraham’s stronger faith.