Going out into the world and seeking new congregants has been a traditional way for many religious institutions to expand their membership, and it is a continuing practice in the modern world. For those who practice a religion where it is expected, their members often choose areas of the world with very different spiritual backgrounds. They see it as an opportunity to bring newcomers into the fold, but some of them find their new flocks are very comfortable practicing several faiths at once.
The majority of religions do restrict their members to only their faith, and they often claim it is the only path to eternal happiness in the afterlife. While not all of them have a strict code that each member practices only that faith, members are encouraged to believe it. In religious institutions where it is mandatory, there have often been checks to ensure people have not reverted to their original religion or chosen to practice multiple ones.
The modern ecumenical movement has partially alleviated this issue, and many faiths have met to discuss their similarities instead of their differences. They have found that cooperating in this way gives them greater access to people, and it allows them to claim members who might also practice another faith. This type of openness has allowed the institutions to find ways to make their members comfortable, and it has solved a number of conflicts between them.
It is not always easy to belong to several different faiths, and it can be difficult for those who have spent a lifetime in only one faith. The modern ecumenical movement has helped smooth the way for conversion, but it has also allowed people to fall back on the comfort of their traditional religious teachings. By accepting the duality, many religious institutions have found their membership increasing as their religious teachings spread.
