"I'm trying to understand Matthew 11.12. Who are the ones trying to take the Kingdom of Heaven by force? Can you please expound upon the meaning of Matthew 11.12?", (Question from Seth).
Matthew 11.12 reads, "And from the days of John the Baptist until now the kingdom of heaven suffereth violence, and the violent take it by force" (Matthew 11.12 KJV bible). This is one of Jesus' more difficult statements, and we don't have a lot in the way of context to help understand it. Here Jesus tells us that the Kingdom of Heaven is under seige, and that violent ones are taking it by force. It also implies that this has been going on since the days of John the Baptist, likely referring to the start of John the Baptist's ministry.
The most common interpretation of Matthew 11.12 is that Jesus is describing a violent rush of converts who are swarming to enter the Kingdom of Heaven. Upon hearing the gospel, these converts are so fervent to embrace the Kingdom that Jesus likens their efforts to a seige. Luke 16.16 is often used as support for this view, "The law and the prophets were until John: since that time the kingdom of God is preached, and every man presseth into it" (Luke 16.16 KJV bible). So the gospel of the kingdom is causing a rush of converts who are desperate to enter it. Therefore, it is not the wicked, but the righteous who are trying to seize the Kingdom.
However, this explanation doesn't work well with the overall language and imagery of Matthew 11.12. The verse describes a siege or takeover in which the Kingdom is resisting those who are trying to control it. It doesn't seem appropriate to compare this violent group trying to seize the Kingdom to the hearers of Christ. Instead of violent aggressors, Jesus compares believers to little children, "...Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven" Matthew 18.3 KJV bible). Matthew 11.12 implies that the Kingdom itself is resisting these violent one's attempts to lay hold of it, and this cannot be applied to the faithful. The faithful have never been trying to seize the Kingdom, but they enter it as little children.
Secondly, there may have been throngs of people that came to hear Jesus and see his miracles. However, it cannot be said of these crowds that they really understood or believed in him, "Therefore speak I to them in parables: because they seeing see not; and hearing they hear not, neither do they understand" (Matthew 13.13 KJV bible). No one can say for sure how many people were spiritually entering the Kingdom, but the scriptures don't support the idea of great throngs crowding their way into it.
To understand Matthew 11.12, we need to consider John the Baptist's ministry. We know that John the Baptist's ministry heralded the coming of Christ, and a new covenant in which Messiah would lead his people, "For this is he, of whom it is written, Behold, I send my messenger before thy face, which shall prepare thy way before thee" (Matthew 11.10 KJV bible). Part of John's ministry was the preaching of the Kingdom of God, "The law and the prophets were until John: since that time the kingdom of God is preached..." (Luke 16.16 KJV bible). John was preparing the way for Christ through both baptism, and the gospel of the Kingdom.
In Matthew 11.12, Jesus is saying that since the beginning of John's preaching, certain individuals had been trying to capture and take control of the Kingdom for themselves. This campaign and siege against the Kingdom was taking place among the corrupt priesthood and religious leaders. These individuals sought to steal away the authority and power of Jesus, and to sit in his place as Messiah.
The people considered John a prophet, but the religious leaders rejected John and his baptism, "And all the people that heard him, and the publicans, justified God, being baptized with the baptism of John. But the Pharisees and lawyers rejected the counsel of God against themselves, being not baptized of him" (Luke 7.29-30 KJV bible). The religious hypocrites refused to justify God in the baptism of repentence, and therefore didn't seek the Kingdom through his will and counsel. They did not enter the Kingdom, but sought to have control of it, "But woe unto you, scribes and Pharisees, hypocrites! because ye shut the kingdom of heaven against men: for ye enter not in yourselves, neither suffer ye them that are entering in to enter" (Matthew 23.13 KJV bible). Rather than seeking to enter as little children, the leaders conspired to undermine and steal the Kingdom through murder and intrigue.
Jesus describes this subversion against him and his dominion through a certain parable. He describes a householder who builds a vineyard, and then lets a group of farmers watch over it while he is away. In time he sends his servants to the farmers to collect the fruits of the vineyard. Instead of receiving them, they beat and kill them. Finally the Lord of the vineyard sends his son, "But when the husbandmen saw the son, they said among themselves, This is the heir; come, let us kill him, and let us seize on his inheritance. And they took him, and cast him forth out of the vineyard, and killed him" (Matthew 21.38-39 KJV bible). Rather than reverencing the Son, they slay him, thinking they will be able to take control of his inheritance.
Similar to Matthew 11.12, this parable describes the religious hypocrites trying to seize what they want through force and violence. They have no inheritance with Christ, but use murder and conspiracy to take control of the Kingdom. They don't care about serving the Lord, but desire power, and use religion as a tool to obtain it. Even now, ones use the name of Christ to try to reign over God's accomplishments, and to sit in places of glory and power. They use religion to exalt themselves, just like the ones who murdered the heir of the Kingdom.