Why did Jesus warn his disciples about Herod?
Herod, the Roman-authorized king ("tetrarch") of Judea, was a ruthless and violent king responsible for the murder of John the Baptist and many others, including his own wife and other family members. Herod was also responsible for the slaughter of children in Bethlehem as he aimed to eliminate Jesus.
Herod claimed to be a follower of Mosaic custom and law - considering himself a rabbi. The Roman Senate declared him, "King of the Jews." Herod also created a false ancestry in an attempt to show himself in line with the great kings of Israel. He also had temples built with his branding and often promulgated on Mosaic law - making it a crime to break Mosaic commandments.
Herod is, in fact, the central reason stonings and hangings were frequent in Judea during those times.
Herod was hypocritical because Herod himself did not abide by the commandments. His murdering of Rabbis such as John the Baptist and others, along with his various murderous acts and acts of indecency were in direct opposition to the commandments of Moses - of which loving God and loving God's children ranked the highest.
What did the Pharisees do?
The Pharisees considered themselves the rightful heirs and interpreters of Mosaic law. They held positions as scribes and temple priests during Jesus' time. They stressed the importance of bathing rituals, extreme sentences, holding slaves, and otherwise forcefully following the ritualistic side of Moses' laws.
The Pharisees were also very vocal in politics and typically held the top spots in local government. They crossed the boundaries between the temple and the state. They were responsible for condemning people to harsh sentences, including stoning and other horrific so-called "eye-for-an-eye" punishments.
According to Josephus and others, the Pharisees considered themselves among the high priestly order. They felt themselves to be in a higher, more superior position than the rest of the population. While they did accept anyone into the priestly order, one had to become approved by the order first.
What does Jesus mean by "yeast"?
Jesus is speaking about their philosophy and their influence over the people of Judea. As temple priests and high priests, the Pharisees claimed to have the true interpretation of the Torah. And Herod claimed himself to be the Messiah, directly in line with the Prophets.
Jesus is stating that neither Herod nor the Pharisees were teaching the Truth. They put themselves into positions of power and authority, yet they were misleading others.
It is this philosophy and influence over others that Jesus is referring to as "yeast." Just as yeast converts flour into dough: The Pharisees and Herod were converting people to their brand of institutional Judaism.
They were spreading their false philosophies just as yeast spreads its influence throughout a batch of dough.
Who chooses God's representative?
Both Herod and the Pharisees were elected or appointed to their posts by committees of men. Yet they were each claiming to be God's representative. They claimed to have the authority to teach about God and represent God's will.
Yet they were each appointed or elected to their posts by men.
Herod was empowered and appointed by the Roman government. He was not commissioned by the Supreme Being as was Moses and the other Prophets, to lead the people. He was appointed and approved by the Roman emperor and the Roman Senate.
The priests were also appointed. The temple pharisee sect created a selection process that appointed those who were politically expedient. This was organized by the chief priest of that region.
Jesus was warning his students to not let these false authority-hungry people influence them.
Jesus also did not want to see his students get wrapped up in the ambition to hold a respected post in the official pharisee organizations. Because he knew this sect was corrupt and their teachers were misleading people.
What was Jesus' principle of empowerment?
Jesus set the example that God's representative was not appointed by a government or committee of men: God's representative is appointed by God and is characterized by following a previous representative of God. This was illustrated by Jesus following John and becoming baptized by John.
If we follow the lives of any of the Prophets we find the same thing. They each mentored under a spiritual teacher before they assumed the position as teacher. Ultimately, it was God who empowered them. But they were guided by God's representative prior to that.
This is the process that Jesus assumed and supported, as Jesus also baptized followers and then told them to also go out and preach on behalf of God. They didn't need to join any group or be appointed or selected by a group of men in order to be empowered. Jesus taught that it was God from within who empowered them to teach:
"But be careful, because they will deliver you up to the councils and in the synagogues you will be beaten, and you will be brought before governors and kings on my account to testify to them. And the Teachings must first be preached before all peoples. But they will capture you and arrest you. Don’t think about what you will say beforehand – nor should you plan: But whatever will be given to you at that time you will speak – because it is not you that speaks, but the Holy Spirit." (Mark 13:9-11)From this we see that Jesus was authorizing his students to go out and preach to others ("And the Teachings must first be preached before all peoples."). They were thus assuming the position of God's representative without having been appointed by any official council of men.
Does this 'yeast' still spread today?
Ironically, these very same conditions and political processes that Jesus warned his students to stay away from are now rampant among many of the institutions that claim to represent Jesus.
For example, a priest or reverend from one of these sects will claim to be God's representative, not because God chose them and they mentored under a previous representative of God, but because a group of men - a council of deacons or cardinals - elected them to their post.
This is the very "yeast" that Jesus is warning his students to stay away from - those who are pretending to represent God but who have simply played politics in order to obtain their elected professional positions within one of these institutions.
This indicates quite clearly that none of these sects actually represent the Supreme Being. The Supreme Being does not have differing opinions or interpretations. The Supreme Being is a Person with a particular will. God is not an issue to speculate upon and create differing interpretations.
We find this element in Jesus' teachings, as he frequently quoted the teachings of the Prophets as he taught his students. Jesus did not invent a new interpretation or a new theory. His teachings followed the teachings of God's representatives who preceded him because there was no contradiction. He was representing God and they were representing God.
Yes, there can be different times and circumstances. But the central message does not change.
The central tenets of Jesus' teachings and the Prophets' teachings - to pray to God, worship God, make offerings to God, and praise God - have remained consistent through the centuries among the teachings of God's true representatives.
Why? Because these methods come from the Supreme Being. They are facilities to gain access to Him. They help us to redevelop our innate yet forgotten loving relationship with Him. This is why Jesus' most important instruction - which quoted Moses' most important instruction - was:
"'Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength.'" (Mark 12:30 and Deuteronomy 6:5)