The restriction of creed is a bit different from those of race and gender as most nations do not actually have laws prohibiting marriage, or any relationship, between people of different religious beliefs. That said, it is a restriction that is still quite real, and one very much responsible for causing untold misery to those who fall in love with ‘the wrong person’.
While most Western societies permit people from different religions to be joined in matrimony, the same cannot be said for many Middle Eastern nations whose governments are of a more theocratic, or religion-based, nature. Many Arab nations, for example, prohibit citizens from marrying outside of the culture, with exemptions only being made on a case-by-case basis, usually by those and for those in the highest levels of government. In other words, the average person can only marry someone of the same culture or face the penalties of prison or worse, depending on the country.
The same restrictions are in place in Israel, where civil marriages aren’t performed. Thus, although Israel will recognize marriages conducted outside of its borders between Jewish and non-Jewish partners, no such marriages are allowed to be conducted within the country.
For the most part, however, the restrictions of creed are less of a legal and more of a traditional situation, recognized only within the specific religion or tradition itself. Persons within the Catholic faith, for example, are strongly discouraged from marrying outside the faith. Although not necessarily forbidden anymore, such marriages cannot be conducted within the physical church, and thus are not recognized as strongly as those between two members of the Catholic tradition. And while such religious restrictions don’t find their way into legislation in more secular-based political systems, they do retain a significant hold on the culture of a country, creating deep-seated taboos to enforce the ideal of ‘pure marriages’. Needless to say, when you pose the question “Who does this protect?”, the obvious and painful answer is ‘no one’. Thus, the control-driven nature of such restrictions is plain to see.