"All Christian denominations are one -- are 'the church'-- because they are united in seeking to follow Christ."

Such an over-devote expression of unity -- spokes in a single common wheel -- implicitly suggests that all believers must pretend/aspire to sentiments of mutual confidence and unity which they do not feel. Just as nations differ in civil and constitutional legislation so do churches differ in doctrinal expressions and canonical customs -- if only for good order and confessional integrity, among other things. Unlimited "unity" doesn't work.