Vows on the 1662 Book of Common Prayer

Would you please explain the meaning of the words of part of the 1662 Book of Common Prayer Holy Matrimony vows:  "For be ye well assured that so many as are joined together otherwise than God's Word doth allow, are not joined together by God; neither is their Matrimony lawful."  This statement seems to me to be the difference between a civil marriage ceremony which has a far different standard to that of a church marriage (Biblical standards) and just because a couple are married in a civil ceremony, does not mean that it meets the requirements for a Biblical marriage.