A.T. Robertson Commentary Matthew 19:6

"So that they are no more two, but one flesh. What therefore God hath joined together, let not man put asunder." — Matthew 19:6 (ASV)

What therefore God hath joined together (ο ουν ο θεος συνεζευξεν). Note "what," not "whom." The marriage relation God has made. "The creation of sex, and the high doctrine as to the cohesion it produces between man and woman, laid down in Gen., interdict separation" (Bruce). The word for "joined together" means "yoked together," a common verb for marriage in ancient Greek. It is the timeless aorist indicative (συνεζευξεν), true always.

Bill (βιβλιον). A little βιβλος , a scroll or document (papyrus or parchment). This was some protection to the divorced wife and a restriction on laxity.