One change created by the Fourth Lateran was in marriage. Prior to 1215, marriage was simply a legal contract between two parties, not a sacrament.* Innocent made it a sacrament, making marriage a much more important bond and presided over by the Church.
He next declared that marriages could not be clandestine: they must be proclaimed publicly ahead of time so that anyone who knows a legitimate impediment against the marriage has a chance to make it known. He warns, however, that lying about such impediments will bring the wrath of the church down on you.
Was this a power grab? An attempt to assert the church's control over political unions? Innocent knew there was bound to be some opposition to "re-defining marriage"; he prefaced his marriage decrees with this:
It should not be judged reprehensible if human decrees are sometimes changed according to changing circumstances, especially when urgent necessity or evident advantage demands it, since God himself changed in the new Testament some of the things which he had commanded in the old Testament.Innocent was pope from January 1198-July 1216, during which he made many changes, some of which are still with us.
*Pre-1215, there were only 5 sacraments: Baptism, Communion, Confirmation, Holy Orders, Last Rites; 1215 established Marriage and the practice of individual Penance at least once per year.