With his parables on the weeds among the wheat, Jesus very realistically teaches us that not everyone will receive the Gospel and its spirit with the same total commitment. Furthermore, individuals who have received the Faith and whole societies which have been Christianized may fall away from a full commitment to the faith or even fall away from it altogether.
Jesus' teaching on divorce is a good starting point for a reflection on this reality. Though Jesus is quite firm on the matter, some individuals and societies keep hoping the Church will change its stance on divorce.
There are, of course, cases where it seems that divorce is the only solution to a marriage which has clearly fallen apart. We do well to remember the teaching of Pope Paul VI: when he re-affirmed the Church's teaching on contraception he also reiterated the need for sensitive pastoral care in dealing with people.
There is a maxim that "difficult cases make bad laws." Though jurists will deny the value of the maxim, there is a certain amount of wisdom in it. A law which tries to provide for every possible difficult case, especially by making concessions, will end up by not being a law at all.
Lord Jesus, give us the grace to be faithful to Your Gospel spirit with joy and peace.