Some churches make membership a category for those few stalwart disciples who will dedicate their entire lives and resources to the church. The rest are welcome to come and participate in the life of the church. They just don't get to become full members until they are really committed. Tithing time and money is not optional for true disciples. United Methodists in general and I in particular view membership more casually.
People join the church as part of their religious pilgrimage.
For some, church membership is an important life commitment. For others, it's just a casual association with an organization that is important only at certain times of the year and for certain occasions, such as weddings and funerals. I am still struggling to make sense of the fact that 15-20 million people in the United States claim to belong to a United Methodist church, and we have only about ten million on our roles many of whom seem barely aware of it. Millions think of themselves as members so casually that they haven't bothered even to tell us about it. I don't suppose this is all bad.