Matthew 22:21-25

Mat 22:21 (KJB)
They say unto him, Caesar's. Then saith he unto them, Render therefore unto Caesar the things which are Caesar's; and unto God the things that are God's.

Caesar demanded taxes to paid to the Roman Empire and here Jesus is taking that coin and showing the people present that one should render unto Caesar what is Caesarís. Caesar represented the things of the world, so he was to be given tribute if required and those things that were legally required such as a Roman soldier could compel a person to carry his goods a mile. This is where Jesus stated if they ask you to go one mile, then volunteer to go two. (Mat 5:41 KJV) And whosoever shall compel thee to go a mile, go with him twain. Then we render unto God, those things that are Godís. Caesar cannot have our eternal soul, our will to obey God over any law which contradicts His law ((Acts 5:29 KJV) Then Peter and the other apostles answered and said, We ought to obey God rather than men.), Caesar cannot have our worship, he cannot have our devotion, etc. This teaches us that there is a limit on our obligation to earthly governments while there is no limitation on our obligation and obedience to God.

Mat 22:22 (KJB)
When they had heard these words, they marvelled, and left him, and went their way.

Then when the people had heard the answer that Jesus gave them, they were astonished at what He spoke. Basically, Jesus was telling them that things which pertain to the secular world are Caesarís but those things which are eternal belong to God. So everyone went their way after hearing the answer given by Jesus. Here is another time they tried to trap Him but they could not.

Mat 22:23 (KJB)
The same day came to him the Sadducees, which say that there is no resurrection, and asked him,

The Sadducees were associated with the priesthood and were in opposition to the teachings of the Pharisees. The Sadducees did not believe in the resurrection, miracles, angels, or spirits. They had rejected the supernatural in their belief system. (Acts 23:8 KJV) For the Sadducees say that there is no resurrection, neither angel, nor spirit: but the Pharisees confess both.

Mat 22:24 (KJB)
Saying, Master, Moses said, If a man die, having no children, his brother shall marry his wife, and raise up seed unto his brother.

This was definitely a set up question because they were heading toward a question concerning the resurrection. What they wanted to do was to take the doctrine of the resurrection and reduce it to a doctrine of irrationality. They only accepted the five books of Moses as official Scripture. (Deu 25:5 KJV) If brethren dwell together, and one of them die, and have no child, the wife of the dead shall not marry without unto a stranger: her husband's brother shall go in unto her, and take her to him to wife, and perform the duty of an husband's brother unto her. They had picked on Deuteronomy 25:5-6 to make this point, however, they extended the Scripture lesson for their convenience.

Mat 22:25 (KJB)
Now there were with us seven brethren: and the first, when he had married a wife, deceased, and, having no issue, left his wife unto his brother:

They extended the example out to seven brethren when the Scripture spoke of one. So begins the procession until they finally get to the last brother.