After having used the mustard seed and shrub/tree idea to speak of God's Kingdom in Mt. 13:31, 32 and Luke 13:18, 19, Jesus later alluded to his own grain of mustard seed picture to describe faith in Matthew 17:20 and Luke 17:5, 6. The record in Matthew dealt with the context of the powerful, spiritual deliverance of a child; the record in Luke presented a marvelous conversation that would be relevant in a simple, down-to-earth way.
The disciples came to Jesus in private. "Why couldn't we cast it [the demon] out?" they asked. "Because of your lack of faith," Jesus replied. "I'm telling you the truth: if you have faith like a grain of mustard seed, you will say to this mountain, 'Move from here to there,' and it will move. Nothing will be impossible for you." (Matthew 17:19, 20 - KNT)
In describing the necessary faith that Jesus clearly had on this occasion, but that the disciples lacked, Jesus alluded back to the image of the grain of mustard, which he had used previously to portray the unstoppable reality of God's coming Kingdom. Faith that is real would be as powerful as the sowing of God's seeded message regarding his victorious future reign. Furthermore, the mustard seed allusion is here connected to Jesus' first use of another striking image: speaking to a mountain to have it moved! Such a picture is certainly suggestive of wonderfully unlimited possibilities!
The record in Luke that alludes back to the grain of mustard seed is highly instructive. There might be a traditional tendency to read Luke 17:1-10 as a disjointed string of four truths, but reading it as a cohesive context reveals great insight into the nature of genuine faith! The context here starts with a solemn warning about not being someone who trips up others. It then proceeds to practical actions in order to avoid being such an obstacle to others. The simple requirement revealed deals with proactive forgiveness if one has been sinned against by another person. (Note, it is not a context about disagreeing with divergent opinions or supposedly perceiving others' flaws!) If one has truly been sinned against, it is appropriate to offer loving rebukes to give the other person an opportunity to repent, apologize, and change his or her attitude. One is to be willing to repeat this process with an individual constantly (seven times a day). This seemingly tedious, never-ending task must have appeared to be daunting for the apostles!
The apostles said to the master, "Give us greater faith!" "If you have faith," replied the master, "as a grain of mustard seed, you would say to this mulberry tree, 'Be uprooted and be planted in the sea,' and it would obey you." (Luke 17:5, 6 - KNT)
The following illustration of a servant simply doing his job, without his master being indebted to him at all, is an integral part of this same conversation.
"Supposing one of you has a slave plowing or keeping sheep out in the field. When he comes in, what will you say? 'Come here at once, and sit down for a meal'? No, you will be far more likely to say, 'Get something ready for me to eat! Get properly dressed, and wait on me while I eat and drink! After that you can have something to eat and drink yourself.' Will you thank the slave because he did what you told him?
"That's how it is with you. When you've done everything you're told, say this: 'We're just ordinary slaves. All we've done is what we were supposed to do.'" (V. 7-10 - KNT)
According to the whole context, what were the apostles supposed to do? They were instructed to avoid tripping up others by wholeheartedly, actively forgiving them! (V. 1-4). This remarkable record takes the reality of genuine faith out of the ethereal realm of artificially pumped up "magic" and places it in the category of simple obedience. If one truly trusts the master, he does what is asked without expecting commendations or applause. In this context, that practical "grain of mustard seed" sown has an overwhelming potential to uproot tenacious obstacles! It is reminiscent of how God's Kingdom, sown as a grain of mustard seed, will not be stopped from ultimately prevailing and providing perfectly for all! In a nearby context, faith is also paralleled with another practical reality: persistently not giving up in prayer, according to Luke 18:1-8.
By the time of the conversation in Luke 17:1-10, Jesus had already emphasized the absolute requirement of forgiving others, ever since his initial sharing of the well-known prayer model in Matthew 6. "Yes: if you forgive people the wrong they have done, your heavenly father will forgive you as well. But if you don't forgive people, neither will you heavenly father forgive you what you have done wrong." (v. 14, 15 - KNT).
At a time pretty near the conversation of Luke 17:1-10, Jesus presented a longer, more detailed discourse about the truths that came out in the brief chat in Luke 17. Matthew, chapter 18, contains that detailed teaching about humbling oneself as a child and being careful to avoid being guilty of tripping up others who believe in the Messiah. The forgiveness discussion here is quite extensive, starting with the illustration of a shepherd committed to rescuing one lost sheep. The discourse goes on to describe loving procedures, even involving the step-by-step help from others to win back someone who has sinned against a person. Forgiveness is to be unlimited, not just seven times but seven times seventy! This teaching scenario culminates with the attention-getting parable of a king who mercifully forgave a servant a huge debt only to see that servant cruelly turn on a fellow servant, refusing to forgive a relatively miniscule debt. The judgement of the king to reinstate the owing of the entire, vast debt is closely made parallel to God's judgement on those who refuse to truly forgive others from the heart!
Whether the Luke 17 chat occurred before or after the major teaching of Matthew 18, it is obvious that Jesus needed to repeatedly focus on bonafide faith by reiterating detailed forgiveness truths with the most powerful imagery possible!
A short time later, having already connected faith like a grain of mustard seed to the power to uproot a mulberry tree (while speaking in Luke 17 about obedience to proactively forgive others), Jesus boldly produced the graphic example of a cursed, literally dried up fig tree! In both Matthew 21:21, 22 and Mark 11:22-24, Jesus alluded back to the picture of removing a mountain that he had used previously in Matthew 17 (the context of the deliverance of a demonized child). That first mountain removal portrayal had also been associated with faith like a grain of mustard seed. In Mark 11, while speaking of real faith and the unlimited, mountain removing potential when believing God in prayer, the reminder to obey God and forgive others is once again reiterated! This faith correlation with the absolute command to forgive others must be supremely important! There is nothing casual about its repeated emphasis.
"Have faith in God,” replied Jesus. “I’m telling you the truth: if anyone says to this mountain, 'Be off with you – get yourself thrown into the sea,' if they have no doubt in their heart, but believe that what they say will happen, it will be done for them. That's why I'm telling you, everything that you ask God for, believe that you receive it, and it will happen for you.
"And when you are standing there praying, if you have something against someone else, forgive them - so that your father in heaven may forgive you your trespasses. (Mark 11: 22-25 - KNT)
Jesus did not allude to previously used imagery in order to force "faith" into the box of a narrow definition; there are many biblical aspects of faith not touched on in this study. Nevertheless, the obedience factor regarding meticulous efforts to actively forgive others cannot be over-emphasized. For example, if one were to isolate certain verses cited here to promote a "name it and claim it theology," the ignorance of certain contextual truths could be deadly. One who would frivolously set out to extract a verse to "claim" a desired result, while hard-heartedly refusing to forgive someone, would be kidding himself or herself. In ancient times as well as modern times, perhaps there has been a sloppy tendency for people to assume that they are loving and forgiving while lightly chalking off those who rub them the wrong way. Jesus' descriptions of painstaking involvement in helping others to be honest, and then constantly forgiving them, seemed like a very difficult task to the apostles. That was in spite of several urgent reminders along these lines!
Faith itself certainly involves confidently being sure of what God has done (since the time He created the universe in six days), what He does now and can do (in unlimited and possibly miraculous fashion), and what He will do (when He will have perfectly revamped His entire creation). There should be no doubt about all this when we seek him in prayer, while being in perpetual awe of His wonderful ways and promises. Faith does not mean the hyped-up inflation of a nebulous factor until one's level of "believing" procures a certain desired result! Sadly, this type of skewed view tends to promote doubt, in which confused seekers stay frustrated until a certain possible answer might arrive! As seen in the network of Jesus' illustrations and allusions, genuine faith, as well as involving an absence of doubt, also means continually trusting God by not slacking off on the nitty-gritty details that He requires, especially when it comes to truly and actively forgiving others from the heart!