What it means to have faith the size of a mustard seed.
The amount of faith or caliber of our faith has no bearing on what constitutes “saving faith.”
There’s an expression of our Lord Jesus that deserves our attention. Not that it has gone unnoticed until now — far from it. Rather, it deserves our consideration and contemplation in light of the “mystery of faith” as revealed in the person and work of Christ (1 Tim. 3:9, 16; Rom. 16:25; 1 Cor. 2:7; Eph. 6:19; Col. 2:2). It’s the saying Jesus that all one needs is a “mustard seed of faith” in order to accomplish the impossible (Matt. 17:20). It goes without saying that this phrase has been grossly misapplied and misrepresented by certain preachers throughout the ages, the likes of which we don’t have time nor space to delve into now. What is the Lord getting at by this saying?
I think there’s no better answer to that inquiry than the following excerpt from Horatius Bonar’s staggering little work, The Everlasting Righteousness, in which page after page exhibits the singular saving merits of Christ crucified. If you’re looking for a treatise that explains the nature of faith and the nature of the gospel — specifically, the gospel of God’s substitution and imputation of righteousness — then Bonar’s achievement in The Everlasting Righteousness is well worth your attention. I turn your attention to this paragraph from chapter 5, entitled, “Righteousness for the Unrighteous”:
The strength or kind of faith required is nowhere stated. The Holy Spirit has said nothing as to quantity or quality, on which so many dwell, and over which they stumble, remaining all their days in darkness and uncertainty. It is simply in believing, — feeble as our faith may be, — that we are invested with this righteousness. For faith is no work, nor merit, nor effort; but the cessation from all these, and the acceptance in place of them what another has done, — done completely, and forever. The simplest, feeblest faith suffices; for it is not the excellence of our act of faith that does aught for us, but the excellence of Him who suffered for sin, the just for the unjust, that He might bring us to God. His perfection suffices to cover not only that which is imperfect in our characters and lives, but the which is imperfect in our faith, when we believe on His name.1
The amount of faith or caliber of our faith has no bearing on what constitutes “saving faith.” The merits and means of salvation are accomplished already in the atoning death of the Lord Jesus Christ. Faith, as small as it is, even as small as a mustard seed, merely claims that work as its own — and therein lies the sinner’s justification. “A mustard seed of faith,” Dan Price says, “can move a mountain of sin and cast it into the sea of forgetfulness.” That’s it. That’s all that’s required. “This is the work of God, that ye believe on him whom he hath sent” (John 6:29). The transaction’s done. “It is finished.”
Grace and peace.
Horatius Bonar, The Everlasting Righteousness: or, How Shall Man Be Just With God? (Carlisle, PA: Banner of Truth, 1993), 74–75.