Mark 12:16-20

Mark 12:16 (KJB)
And they brought it. And he saith unto them, Whose is this image and superscription? And they said unto him, Caesar's.

They brought Jesus the coin and then Jesus asks them about whose picture was on the coin and the inscription? There would be a picture of whichever Emperor was reigning and a brief inscription about him. In this case it would have been Tiberius who reigned from 14-37 A.D. The superscription would have read, “TI CAESAR DIVI AUG F AUGUSTUS” which translates “Tiberius Caesar, son of the divine Augustus.” Actually the Jews had denounced pictures on the coins because they claimed it was an engraved image and a violation of the second commandment. So they answered Him saying it was Caesar’s.

Mark 12:17 (KJB)
And Jesus answering said unto them, Render to Caesar the things that are Caesar's, and to God the things that are God's. And they marvelled at him.

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 Caesar’s. 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 God’s. 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.

Mark 12:18 (KJB)
Then come unto him the Sadducees, which say there is no resurrection; and they asked him, saying,

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.

Mark 12:19 (KJB)
Master, Moses wrote unto us, If a man's brother die, and leave his wife behind him, and leave no children, that his brother should take 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.

Mark 12:20 (KJB)
Now there were seven brethren: and the first took a wife, and dying left no seed.

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.