Not always so abstract.
Point of history: This was the case with the California Missions too. The Franciscans built them in the days of Spanish rule (when Mexico, including much of California, was part of Spain). When Mexico became independent, the California Missions were secularized – that is, the missions were shut down and re-opened as schools, marketplaces, and other non-religious purposes. (Sound familiar? See: Gospels, also Maccabees.)
It’s always better to preserve historic structures even if only for their historical importance. But also there can be the hope that the structures will be restored to their original purposes too.
Shortly after California became part of the United States, Abraham Lincoln signed the papers (I don’t know if it was a law Congress passed or an Executive Order), giving the missions back to the Franciscans. To this day, most of the old missions (with a few exceptions) are functioning missions, run by the Franciscans. Many of them also include museums now, too.