"We must explain how the new emerged from the old..."  I cringe on this one, because one side backs the "opposition" into a corner, so that what may once have had some "wiggle room" becomes written in detail in stone.  I think it is going to be difficult for the Church to "develop" doctrine on contraceptives, women priests, the LGBT people as part of God's creation that is "good," etc.  What Pope Francis has run into in trying to include divorced/remarried more in the life of the faith is an example.

Yes, the new does emerge from the old - culture changes, knowledge grows.   Women who use contraceptives (new knowledge), for example, aren't always or necessarily refusing a gift of fertility but are focusing on expressing other gifts now that they are allowed to (cultural change).   Contraceptives allow women to manage their fertility, to better focus their lives.  They are not obstinately disobeying "the rules", but are seeking a life not anticipated by the rules.  

See Comment #2