In the Old Testament, when a married man died, if he had no children, his brother was expected to marry the widow. The first child born to that second union was named after the first husband so that man’s family name would not disappear (Deuteronomy 25:5-6). It was to this law the Sadducees were referring in Mathew 22:23-28).
Jesus told them they had missed the purpose of the law. The purpose of maintaining family names was to keep the blood-lines distinct. The Messiah was to come from Judah. If records were lost, how would the people know a prophecy had been fulfilled? In other words, the law had only to do with the fulfillment on earth, not of how things function in heaven.
The concept of brother-in-law marrying a widowed sister-in-law is foreign to us, but we also tend to interpret scripture according to our culture and times. It is important that we understand the full word of God and not attempt to put heavenly meanings to earthly things (i.e. wealth, success).
