duh...it's through God
check out Ephesians 2:14-15
Paraphrasing: For He himself has made the two one (unity) and has destroyed the barriers (family ideologies) and the dividing wall of hostility (who has what, keeping up with the Joneses) by abolishing in his flesh - disharmony of any kind (marriage, body of Christ, racial, politics) is grounded in the flesh.
I know this main intent of the aforementioned scripture is primarily for the division between Jews and Gentiles, circumcised & uncircumcised (or those that are in the covenant and those out of covenant), but this is exactly what marriage is: entering into a covenant.
Ecclesiastes 4:12b says "A cord of three strands is not quickly broken." He, God, is the 3rd strand who makes two opposites into one.
How does the two become one? Allow the Master more in your heart and accept the finished work of Calvary (beginning with He has made the two one).
Have a great day!