Q. Why will there be no marriage in Heaven?
A. Because God's institution of marriage, Genesis 2:24 , is not a means to an end in itself. It is a copy/type of Christ's relationship with the church, the 'mystery' revealed by Paul in Ephesians 5:31&32.
'"Therefore a man shall leave his father and mother and hold fast to his wife,
and the two shall become one flesh." The mystery is profound, and I am
saying that it refers to Christ and the church.'
As Christ will be with His church when the world is made new, there will be no need for the copy, no need for marriage.
Thanks Piper - why couldn't anyone have explained it that simply before.