“Either make the tree good and its fruit good, or make the tree bad and its fruit bad, for the tree is known by its fruit. You brood of vipers! How can you speak good, when you are evil? For out of the abundance of the heart the mouth speaks. The good person out of his good treasure brings forth good, and the evil person out of his evil treasure brings forth evil. I tell you, on the day of judgment people will give account for every careless word they speak, for by your words you will be justified, and by your words you will be condemned.” (Matt 12:33-37)
The passage above is actually the tail end of Jesus' comments regarding the 'unforgivable sin', but I decided to include them here because there is a connection between the two passages.
Jesus' builds on his condemnation of the Pharisees by pointing out the source of the accusations they have been making against him. It is a truth he will return to on more than one occasion - what defiles us comes from inside us. Just as a bad tree cannot produce good fruit a person whose fundamental heart condition is evil cannot be a fundamentally good person. Our world view is formed by our spiritual foundation, what Jesus calls our "treasure". When this treasure is corrupted how we perceive the world around us will be shaped by that corrupted treasure. It is why the Pharisees suggested Jesus was working by the power of Satan, and it is why they come up with this next brilliant request.
Then some of the scribes and Pharisees answered him, saying, “Teacher, we wish to see a sign from you.” But he answered them, “An evil and adulterous generation seeks for a sign, but no sign will be given to it except the sign of the prophet Jonah. For just as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth. The men of Nineveh will rise up at the judgment with this generation and condemn it, for they repented at the preaching of Jonah, and behold, something greater than Jonah is here. The queen of the South will rise up at the judgment with this generation and condemn it, for she came from the ends of the earth to hear the wisdom of Solomon, and behold, something greater than Solomon is here. (Matthew 12:38-42)
On the surface, this seems like a ridiculous request. They've seen the sight restored to the blind, hearing to the deaf, demons cast out and many other miraculous events; there is a temptation to ask,"What more of a sign do you need?" And this is the take most commentators make on this passage. But I think we take this attitude because we regard this question as a separate event. But what if it is actually a part of the preceding conversation?
Let's sum up the sequence. (a) The Pharisees accuse Jesus' of casting out demons by the power of Satan. (b) Jesus' responds by pointing out that Satan can't do that because he'd be opposing himself, and the Pharisees should know this. (c) He then warns them about the danger of blaspheming the Holy Spirit and points out that this kind of thinking can only come from a heart that is inclined towards evil. (d) Then as if to punctuate Jesus' point, the Pharisee's come back with, "Give us a sign" or in a more modern vernacular "Prove it!"
I think the Pharisees request for a sign is not a failure to recognize the miracles as 'signs', but rather it is their response to Jesus declaration that only God could be empowering the miracles Jesus has been performing. If they just accept his argument on it's own merits then they also have to accept what he has said about themselves, that their motives are fundamentally evil. This of course is not an option. So they resort to an age old method of philosophical debate; they ask for proof!
In a more verbose edition of the request the Pharisees are saying, "Prove to us that what you are saying is true. Give us a sign! Your argument that Satan can't cast out Satan is an interesting one, but how do we know you're right? Maybe you're just trying to turn this argument back on itself to put us on the defensive. So... give us a sign! Prove to us that you are from God!"
If it were coming from an honest place of inquiry this would not be an outrageous request, but Jesus knows that the Pharisees are responding from fear; fear of losing their position and power. It is for this reason that it is an evil and adulterous generation that seeks for a sign. They seek signs not to prove that God is at work in the lives of men, but to prove that he is not. Those who believe require no proof; their faith is all the proof they need. It is only those who hold to a godless world view and want to see it stay that way who ask for proof.
And so Jesus offers them a sign, but not the kind of sign they were looking for. The sign of Jonah - three days and nights in the belly of the earth. He is of course referring to his death and resurrection. Those same individuals who ask for a proof they don't really want to see, will make much of the fact that Good Friday afternoon to Easter Sunday morning don't add up to three days and nights. They can't handle the idea that Jesus is simply making use of metaphor because again they are splitting hairs because they don't want to believe.
If Matthew chose the more poetic "three days and nights" to the more precise "two days, two nights and a bit" - what of it? The resurrection is not rendered null and void if it happens a few hours earlier than expected. An honest heart does not say, "Well, you are here Jesus, a few days after your death, as you promised, but the timing was off and so I have to question whether you actually came back to life at all." Such logic comes from a very empty place which is the subject of the final portion of this passage.
“When the unclean spirit has gone out of a person, it passes through waterless places seeking rest, but finds none. Then it says, ‘I will return to my house from which I came.’ And when it comes, it finds the house empty, swept, and put in order. Then it goes and brings with it seven other spirits more evil than itself, and they enter and dwell there, and the last state of that person is worse than the first. So also will it be with this evil generation.” (Matthew 12:43-45)
There is a saying that goes, "Nature abhors a vacuum." So, it would seem, do demons. But seriously, this entire line of conversation is summed up in this one paragraph. The entire position of the Pharisees is one borne, not out of faith in God, but out of a moral vacuum that leaves them open to all the temptations of power and position.
When one's moral code is founded only on what will maintain the status quo, or what will benefit me the most, then there is no limit to the hateful and even evil things we might say in defense of our position. Many times I have seen those desperate to defend an indefensible position dig themselves deeper and deeper until there is simply no way out.
The worst part is they often are fully aware that their position is untenable, but their fear of admitting to being wrong is so great that they will go to their deaths defending something they don't truly believe. And this I think is the greatest tradgedy of all. For when our fear of being wrong is greater than our fear of eternal damnation, then where is forgiveness to be found?