To understand why Bethany regularly includes two preludes, you need to consider the role or purpose of the prelude. There are at least two different perspectives:
1. The prelude is "background music" that creates an inviting atmosphere as people arrive for worship. In other words, it's okay to pay little attention to it while we take off our coats, greet friends, and scan the bulletin announcements before the service.
2. The prelude should be a time for prayer, reflection, and preparation for worship.
At Bethany, the worship and music committee felt the second philosophy was an important aspect of worship. For that reason, the prelude was played after pastor made the announcements and asked us "To prepare our hearts and minds for worship" during a brief prelude.
However, that created the dual problems of limiting the prelude to pieces of approximately one minute, while also creating an awkward period of silence as congregants arrived. This problem was addressed by creating a pre-prelude. Now, Tom is free to play more substantial pieces from the organ literature as people are arriving, fulfilling the first goal of the prelude. Then, after the announcements, the second prelude provides a transition from the ordinary business of life to the sacred environment of worship.
I don't know of any other church with this unique format, but I've grown to like it a great deal. I particularly like the freedom to program organ literature in the first slot, while reserving the second slot for short pieces that relate to the hymns for the day. I'd love to hear reactions both from members and from others reading about this for the first time.