Context is essential in understanding this passage. The Sadducees were a religious party who were at loggerheads with the Pharisees over many issues, but one of the main divisions was over the resurrection of the dead, as they treated the first five books of the Bible- the Pentateuch- with the greatest seriousness and did not accept any of the oral law and tradition beloved by the Pharisees. The Sadducees did not believe in any kind of after life and so they approached Jesus with a trick question designed to buttress their views. It is also essential that we understand what the Jewish Laws were concerning re-marriage in the event of the husband's premature death. If you have studied the beautiful book of Ruth you will have noted a very strange arrangement in chapter 4 verses one to ten and this demonstrates the part of the Law which stated that if a married man dies then his wife is to marry his brother- Deuteronomy 25 v 5-10. The Sadducees magnify this tragic situation to farcical heights by insisting in their tale that this takes place seven times!
In answering this group, Jesus demonstrates how paltry and badly put together their story is. Firstly, He makes it clear that in the resurrection, the old laws of physical life such as marriage no longer will exist. The life to come will bear no relation to this life at all.
Secondly, Jesus deals with the fact of the resurrection. The Sadducees' case against the resurrection was that it gave no mention of this in the Pentateuch and so Jesus draws His evidence from these books. With consummate skill, He replies that there is ample evidence and quotes Exodus 3 v 6 to substantiate His case. When God meets Moses in the burning bush, He pronounces that He is the God of Abraham, the God of Isaac and the God of Jacob, and so states that they are still alive and if the patriarchs are still alive then the resurrection is proven!
What this says to us is that we can become wildly in error if we content ourselves in taking the views of others uncritically. We must study the Bible for ourselves! Secondly, we must understand that the resurrection life will be entirely different from this one and any attempt to describe what it may be like will fall well short of the reality.