The Sadducees were members of a Jewish priestly sect that denied the resurrection of the dead. They hope to stump Jesus with their hypothetical case of one wife of seven brothers so as to show how ridiculous it was to believe in the resurrection of the dead. If Jesus, the great Teacher were stumped then their theological view (that there is no resurrection) would be established.

Their question was based upon the teaching and practice of levirite marriage (Deuteronomy 25:5-6).

5 If brothers are living together and one of them dies without a son, his widow must not marry outside the family. Her husband's brother shall take her and marry her and fulfill the duty of a brother-in-law to her.
6 The first son she bears shall carry on the name of the dead brother so that his name will not be blotted out from Israel.

The purpose of the levirate marriage law was to enable a man who died before fathering an heir to obtain one and so perpetuate his name and estate. “Levir” means husband's brother.

The Sadducees were probably contending, “If there is a resurrection of the dead then there is no need for levirate marriage to perpetuate the name of the dead! Conversely, Deuteronomy 25:5-6 seems to suggest that the way of immortality is the perpetuation of a man’s name through a son. Therefore, there is no resurrection.”

Jesus replied that in the kingdom age of the resurrection of the dead, there will be no marriage (consequently, no reproduction of children) and no death. Thus the hypothetical case would be non-existent. Jesus cited Exodus 3:6 to affirm that the dead do rise. Moses spoke of God as the God of Abraham, Isaac and Jacob (all of whom had died) and since God is the God of the living, then God could only be their God if they would rise from the dead eventually. 

Spiritual Exercise: There is resurrection from the dead but there is no reincarnation after death. Man is destined to DIE ONCE, and after that to face judgment by God (Hebrews 9:27). There is no second chance after death. Are we ready to face our Creator and Judge? If you knew you had only one more year to live, what would you do? What kind of legacy do you want to leave behind? What steps do you need to take now for that to happen?

Prayer: 
The length of our days is seventy years —
or eighty, if we have the strength;
Teach us to number our days aright,
that we may gain a heart of wisdom and
die satisfy with life.