Matthew 17:20 in the King James Bible reads, “And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.” Its meaning becomes clearer when it is heard within the moment that provoked it, the spiritual condition it exposes, and the images it deliberately chooses to teach what faith is and what unbelief does.

The immediate context is a failure. Just before this saying, a father brings his afflicted son to the disciples, and they cannot heal him. When Jesus comes, He rebukes the devil and the child is cured “from that very hour.” Then the disciples, privately and with the humility of those who know they have come up short, ask, “Why could not we cast him out?” Matthew 17:20 is Christ’s answer to that question. The point is not that the disciples lacked information or technique, but that something in the inward posture of their hearts had become deficient: “Because of your unbelief.” In this setting, “unbelief” is not mere intellectual doubt as a passing thought; it is a spiritual deficit that weakens obedience and makes them prayerless, timid, or self-reliant in a work that requires dependence on God. The verse therefore speaks about the difference between possessing a calling and operating in living trust. It is possible to be among the disciples and yet, at a particular hour, act as though the power is human rather than divine.

From there Christ turns from diagnosis to promise, introduced with the solemn phrase, “for verily I say unto you.” He ties the remedy not to a dramatic quantity of faith but to its reality. “If ye have faith as a grain of mustard seed” is a carefully chosen symbol: the mustard seed is small, unimpressive, easily overlooked. In the imagery of Scripture, it does not represent a faith that is elaborate or showy, but a faith that is genuine and alive even when it feels little. The seed is also an image of something that contains life within itself and is meant to grow. Christ is not glorifying spiritual smallness for its own sake; He is teaching that the smallest true faith, because it is faith in the true God, is of a different kind than mere human confidence. The disciples were facing a problem larger than their apparent spiritual stature, and Christ tells them that the issue is not that the obstacle is too large, but that their trust has been too compromised by unbelief to lay hold on God as they should.

The saying about the mountain intensifies the lesson: “ye shall say unto this mountain, Remove hence to yonder place; and it shall remove.” “This mountain” is not only a picture of something immense; in the narrative it functions as a symbol for what appears fixed, immovable, and beyond human ability. Mountains in Scripture often represent stability, permanence, and insurmountable barriers. By selecting that image, Christ sets the contrast between what human effort cannot budge and what God can do when faith is present. The act of speaking to the mountain suggests authority exercised under God, not magic words. In other words, Christ is not teaching a verbal formula but the spiritual reality that faith expresses itself confidently because it relies on God’s power and God’s will, not on personal strength. The disciples tried to deal with a grievous case and found their weakness; Christ points to the kind of dependence that does not buckle when confronted with something intimidating.

Yet the verse must be understood with the balance of Scripture itself. “Nothing shall be impossible unto you” is not a blank check for self-directed desires; it is a statement about the scope of what God can do through believing servants when they act in submission to Him. In the immediate story, the “impossible” refers to deliverance from an oppressive power they could not overcome. Christ’s words are therefore aimed at ministry, obedience, and the accomplishment of God’s purposes rather than personal spectacle. The disciples are being drawn back to the truth that the work is God’s, and that their part is faith—real trust, real prayer, real dependence—rather than presumption.

There is also a quiet theme of reproof and restoration. Jesus does not discard them for their failure; He teaches them why they failed and calls them upward. The private nature of the disciples’ question and Christ’s direct answer show that He is forming them. Matthew 17:20 therefore carries pastoral weight: it exposes unbelief as the root of spiritual impotence, and it encourages those who feel small that God does not require a grand, perfected faith before He works, but a true faith that looks away from itself to Him.

The verse also sits within the larger movement of Matthew 17, where glory and weakness are placed side by side. Earlier in the chapter, Christ is transfigured, revealing His majesty; soon after, the disciples cannot cast out a devil. The juxtaposition teaches that the kingdom of God is not advanced by human capacity but by divine power received through faith. The mountain-moving promise is thus not an invitation to boast, but an invitation to rely. Faith as a mustard seed is powerful not because the seed is impressive, but because faith connects the believer to the living God, before whom the “mountain” is not ultimate.

In sum, Matthew 17:20 teaches that unbelief can render God’s servants ineffective, that even small but genuine faith is mighty because of the God it trusts, that the “mountain” symbolizes obstacles that appear immovable, and that the promise “nothing shall be impossible unto you” speaks to the limitless ability of God at work through obedient faith. It calls the reader away from self-reliance and toward a faith that, however small at the start, is real, dependent, and therefore able to witness God do what human strength cannot.