Why do we do temple marriages if in the bible in Matthew and Luke it says there will be no marriages in heaven?
That is specifically why we do marriages in the temple. There is no baptism in heaven either. All the ordinances of the gospel are to be performed during mortality. And when they are performed under the authority of the holy priesthood and the recipients of the ordinances honor the covenants of which the ordinances are a sign, they are valid in heaven and throughout the eternities.