Hi Elna,
A bit later, because it was very warm here last days,
but about your question: I don't kwown very well the exact details en reasons , but indeed in that time it could give problems when a catholic person wanted to marry a protestant person,
perhaps you can find more about it on the English Wikipedia site, maybe here f.e:
http://en.wikipedia.org/wiki/Religion_in_the_Netherlandsregards, Jettie