The Lord Jesus returned to Galilee to the region of Magadan (chapter 15:39: this place was unknown to early students or copyists, so they changed it to the familiar Magdala), next to Dalmanutha (Mark 8:10) and He was soon sought by the Pharisees and Sadducees.
Sometime before some of the Pharisees and scribes had asked him to make a miraculous sign before them (chapter 12:38), and His reply was that no sign would be given them, except the sign of the prophet Jonah. He was referring to His death and resurrection.
This time, another group had gathered to test Him: it consisted of Pharisees and Sadducees. From the doctrinal point of view, they held opposing convictions:
The Pharisees prided themselves on fulfilling the letter of the law given through Moses and to believe and obey the writings of the prophets, to which they added their own regulations. The Pharisees not only added their tradition, which submitted the people to more obligations than those required by the Law of Moses, but they were also notorious for their hypocrisy, ritualism, false piety and bigotry. They hated the Lord Jesus because He brought down their fake religiosity, saw their thoughts and knew their wicked hearts, comparing them to "whitewashed tombs": appearance of piety on the outside, but full of malice on the inside.
The Sadducees were aristocrats among the priests, considering themselves higher authorities, judging themselves able to criticize the Word of God. Thus, they accepted the Torah (Pentateuch) but rejected all other Scriptures. Denying the existence of angels (good and bad), the immortality of the soul and therefore the resurrection of the dead, according to the Sadducees the human being was limited to physical life, receiving here the reward and the punishment for his actions. They denied eternal punishment. They hated the Lord Jesus because He destroyed all the authority that they had assumed, confirmed not only the Pentateuch but also everything that was written in the Scriptures, His teachings were mainly spiritual and informed about spiritual creatures, the eternity of the soul, and the divine judgment after physical death. All the falsehoods that they taught were thus exposed.
Although the Pharisees and the Sadducees hated one another because their doctrines were diametrically opposed, this time they joined to face their common enemy, the Lord Jesus. They hated Him even more than they hated each other. Together, then, they challenged Him to show them "a sign from heaven".
What they wanted is not known exactly: would it be a supernatural phenomenon visible in the sky, since all the signs that He had done had been on earth? Alternatively, putting into doubt the origin of the signs already made, as they did on the occasion of the healing of the demon-possessed man (chapter 12:24), did they want a sign that clearly proved the divine origin of His power?
The Lord knew they were all unbelievers and their request was a trap to discredit Him. He pointed to their folly, because although they could interpret the aspect of the sky to indicate the weather depending on the time of day, their unbelief did not allow them to see the reality of His divine person.
The signs of the times, which they did not know how to interpret, were:
The fulfilment in His person of dozens of promises about the coming of the Messiah found in the Old Testament.
The coming and preaching of John the Baptist.
All the signs that He had given indicating His power and His authority.
All His teaching, which surprised the people, again demonstrating the authority and wisdom that He had (and was causing most envy to these false teachers).
The Pharisees and the Sadducees were blind, they saw the evidence before them, but they refused to perceive it. With hypocrisy, they now approached the Messiah and pretended to want to see more evidence.
He repeated again that they were "a wicked and adulterous generation", and that He would give them no other sign except that of the prophet Jonah (see Jonah 3:4, and the comments on Matthew 12:33-45 under the title "The condemnation of the Pharisees").
This perverse and spiritually adulterous generation would eventually crucify the Messiah of Israel who they rejected, but He would rise again, triumphantly, on the third day, thus giving them the "sign of the prophet Jonah"- the greatest sign of all - to confirm His divine identity. The Lord Jesus then withdrew again from Galilee, going to the other side (Mark 8:13). Therefore, He literally distanced himself from those men.
The disciples forgot to take bread, having only a loaf to share between them. So, when the Lord told them to be vigilant and beware of the leaven of the Pharisees and of the Sadducees, they thought that he was referring to the need to purchase bread that was not contaminated by the leaven from those people.
Like them, we run the risk of sometimes interpreting materially what is spiritual in nature. How many believers were martyred because they correctly denied that the “bread” and the content of the “cup” at the Lord's Supper became physically the body and blood of the Lord Jesus (a dogma of “catholic” and “orthodox“ institutions).
Seeing that His disciples were arguing about this, the Lord rebuked them, saying that they were men “of little faith". After having twice watched and participated in the multiplication of loaves to crowds, how could they fail to understand that He was not talking about material bread? He had been referring to the teaching of the Pharisees and Sadducees, and the disciples now understood the reason, because they knew them very well. The leaven is evil and malice in 1 Corinthians 5:6-8, generating perversity like that of the Pharisees. Leaven is also false teaching, as we read in Galatians 5:9.
The Lord had told them the parable of the leaven, which a woman put in three measures of flour and ended up contaminating the whole mass (Chapter 13 verse 33). This is similar to the Kingdom of God, subject to contamination by the enemy, who puts in the elements to corrupt it. We have been warned, so we must not be surprised with the wide variety of institutions taking all sorts of denominations, some huge and powerful, all calling themselves Christian, but teaching things completely unrelated to the Word of God.
Pharisaism is notorious in many “churches” who dare to claim they are "Christians", but, on the contrary, they are apostate and heretical, enemies and persecutors of true believers in Christ. They pretend to be Christian, but do not even know the Lord, much less obey Him. However, they cover themselves with a religiosity, which is oppressive, deceiving and exploiting of those who are in them.
Others, like the Sadducees, consider that they have the freedom to make a "rational" analysis of the Word of God, separating to their taste texts that suit them and abandoning the rest. They come even to doubt supernatural facts found in the Bible, going down a path that leads to the total disbelief.
Thus, so-called "Christianity" today is all contaminated, it has lost its flavour, and in it the enemy makes his nests. The leaven of the Pharisees and Sadducees has completed its work.
There is a positive side, however: we must consider ourselves very fortunate because we easily have at our disposal the very source of all legitimate Christian doctrine, the Word of God, printed and purchased cheaply on paper, and available freely in electronic form on the Internet. Let us satisfy ourselves with it, and let us follow Christ only.
1 Then the Pharisees and Sadducees came, and testing Him asked that He would show them a sign from heaven.
2 He answered and said to them, "When it is evening you say, 'It will be fair weather, for the sky is red';
3 and in the morning, 'It will be foul weather today, for the sky is red and threatening.' Hypocrites! You know how to discern the face of the sky, but you cannot discern the signs of the times.
4 A wicked and adulterous generation seeks after a sign, and no sign shall be given to it except the sign of the prophet Jonah." And He left them and departed.
5 Now when His disciples had come to the other side, they had forgotten to take bread.
6 Then Jesus said to them, "Take heed and beware of the leaven of the Pharisees and the Sadducees."
7 And they reasoned among themselves, saying, "It is because we have taken no bread."
8 But Jesus, being aware of it, said to them, "O you of little faith, why do you reason among yourselves because you have brought no bread?
9 Do you not yet understand, or remember the five loaves of the five thousand and how many baskets you took up?
10 Nor the seven loaves of the four thousand and how many large baskets you took up?
11 How is it you do not understand that I did not speak to you concerning bread?—but to beware of the leaven of the Pharisees and Sadducees."
12 Then they understood that He did not tell them to beware of the leaven of bread, but of the doctrine of the Pharisees and Sadducees.
Gospel of Matthew, chapter 16, verses 1 to 12