What. The unity, not "those" (the persons).
God. App-98.
hath joined together, &c.. joined together, &c. The converse is true also. See note on Philippians 1:1; Philippians 1:10.
Related Commentaries of Matthew 19:6
Matthew 19:6
6 Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.