Weird name? Sure. Important Symbol? Definitely.
Herbert was a student of comparative religion and "drew on a variety of religious influences without adhering to any one of them" (Afterword.14). The result of his study into many diverse religions is the Orange Catholic Bible.
The Orange Catholic Bible is a holy book combining many different religious texts, including "Buddhism, Sufi Mysticism, and other Islamic belief systems, Catholicism, Protestantism, Judaism, and Hinduism" (Afterword.14). It even includes some religious texts Herbert fabricated to increase the historical breadth of his futuristic society.
The purpose of the Orange Catholic Bible is to combine all the religions in one place so that Herbert can write about religion as a whole rather than single just one out. When the novel portrays religion's effect on politics and society, it's trying to say that this effect is true of all religions in all eras. As a result, the Orange Catholic Bible becomes both an invaluable source of wisdom and also a precarious source of political and cultural strife.
Match Made in Heaven
Oh, and as for that odd name. The orange in the name is derived from the orange flag the Protestants flew during the Northern Irish Conflict. The violence between the Catholics—who flew a green flag—and Protestants—who flew an orange—erupted in the '60s and was a topic of much discussion. The name suggests the bringing together of these two conflicted social and religious identities.