Christianity does not exist apart from being expressed in specific people at specific times. There is no version of Christianity so “above” culture that it can be pulled down and plugged into a new setting without adapters. With that, mixing and matching Christian teachings and traditions is very healthy for the life of any given denomination or tradition. Investigating other Christian traditions gives a good idea of the essence of “mere” Christianity, saves theologians from intellectual inbreeding, and restores atrophied parts of a Christian’s own tradition.
Mixing and matching is for personal benefit and not for the sake of offering something to the world. As great as building a theological consensus can be, it is no good for pressing flat the wrinkles and creases in Christian theology. Traditions are like libraries, so watch out for the dusty books on the top shelves of forgotten corridors: there is more in heaven and earth, Christian, than is dreamt of in your theology. In Harry Potter, there are hunts for rare potion ingredients, whether it is stealing boomslang skin from Snape’s supply closet or sneaking a bit of acromantula venom from Hagrid’s dead monster spider friend. This is Christian mixing and matching. In business terms, it is a search for new suppliers and not new buyers. Other traditions may teach students from beyond their fold, but it is for the student to study, finish their dissertations, and let the teachers go on about their business.
Studying other Christian traditions helps Christians know their own traditions and the ways that they need to evolve. Studying the Christian and Missionary Alliance and how it sprang from Presbyterianism gives lessons on the need to reinvigorate missionary traditions before denominational splits occur. Dedicated study of Lutheranism teaches how Christians can keep elements of old tradition and strive for Christian unity while standing for the good of the Reformation. Calvinists have robust theology, and their focus on the glory of God inspires others to make church relevant to God rather than the odd non-churchgoer. Denominational lineage helps Christians to place their church on the correct branch of the family tree and it shows what traditions they might look to in order to get a fresh but harmonious perspective on theology and practice.
For Christians sampling various traditions, it is important to consider the distance that they have traveled from their home traditions. Protestants reading from Catholic mystics like St. John of the Cross and Ramon Lull (also known for missionary activity in the Muslim world), Protestants at least share Western European history and culture. Looking into Eastern Orthodoxy and Patristic writings brings in cultural and historical distance. Eastern Orthodoxy never had to grapple with the Reformation in the way that Roman Catholicism did, Roman Catholicism never had to deal with Muslim domination in the same way that Eastern Orthodoxy did, and Eastern Orthodoxy dealt with the problem of papal supremacy in 1054, five centuries before the Reformation was in full swing. Stepping outside of familiar streams of Christianity is wading in a strange and flowing river, not just taking a dip in a still and motionless pool.
Exploring other Christian traditions is best used to know what to look for in the hall closet at home rather than to find the best hall closet for your personal tastes. Closets are the kind of thing that you cannot change without buying a new house, so unless you want the new house, diving into a friend’s closet is only useful as far as it reminds you of that awesome gorilla suit collecting dust at your house. For Protestants, they can look to the Lutherans if they want a Protestant perspective open to using images in worship. Iconography in Catholicism and Orthodoxy has extensive theological frameworks that keep explorers from wrenching it out of place and using it in their home churches. For Catholics, they can look to the Spanish mystics if they want something on knowing God personally and save themselves from anti-Catholic polemics. Seeing good things in other traditions reminds Christians about atrophied parts of their own traditions, and unless they want to join another tradition, they should try to help their home tradition be the best that it can be.
Mixing and matching from different Christian traditions is great. The American Kennel Club might turn up its nose at the mutt’s pedigree, but that beautiful golden retriever will go to the vet (if not the morgue) if it eats what it finds behind the dumpster. The best members of any given denomination are those who have come to grips with the differences around them, rather than those who know only what they have at home. Conversely, some of the worst Catholic and Orthodox believers are grumpy ex-Protestants who can find nothing good in what they left. There is a reason why mongrels and mutts are greeted with a good kick. Perhaps it is better to have a purebred dog in the first place: at least we know what its issues might be before we take it to the vet. Who knows what cancerous casserole the animal shelter adoptee ate five years ago? Read a lot, talk a lot, listen a lot. There is more to gain than to lose in dialogue, but do so with an eye toward improving your own house rather than mine.