And Sadducees came to him, who say that there is no resurrection. And they asked him a question, saying, “Teacher, Moses wrote for us that if a man’s brother dies and leaves a wife, but leaves no child, the man must take the widow and raise up offspring for his brother. There were seven brothers; the first took a wife, and when he died left no offspring. And the second took her, and died, leaving no offspring. And the third likewise. And the seven left no offspring. Last of all the woman also died. In the resurrection, when they rise again, whose wife will she be? For the seven had her as wife.”

Jesus said to them, “Is this not the reason you are wrong, because you know neither the Scriptures nor the power of God? For when they rise from the dead, they neither marry nor are given in marriage, but are like angels in heaven. And as for the dead being raised, have you not read in the book of Moses, in the passage about the bush, how God spoke to him, saying, ‘I am the God of Abraham, and the God of Isaac, and the God of Jacob’? He is not God of the dead, but of the living. You are quite wrong.”
Mark 12:18-27.

The Sadducees only believed in the material world. No angels, no resurrection. So their hypothetical situation is something they don't even believe in. It is a question designed to come up with no good solution. But Jesus takes the position of Moses, the very authority they are using to trip Him up. Abraham,  Isaac,  and Jacob are still alive in a different place, like the angels.

There are laws that apply on earth that are different from those in heaven. Man was given the earth to rule over it. When man sinned, the earth was put under a curse. God rules over a heaven where there is no sin and no curse. Man was told to multiply and fill the earth. He has no such jurisdiction in heaven. 

Thus is why we are to set our eyes on things above. They are eternal, whereas the things of this world are passing away. "Do not love the world or the things in the world. If anyone loves the world, the love of the Father is not in him. For all that is in the world—the desires of the flesh and the desires of the eyes and pride of lifec—is not from the Father but is from the world. And the world is passing away along with its desires, but whoever does the will of God abides forever." (1 John 2:15-17).