Sentence:  A perfectly drilled wedding procession, like a military one, should move forward in perfect step, rising and falling in a block or unit. To secure perfection of detail, the bars of the <WSD>processional</WSD> may be counted so that the music comes to an end at precisely the moment the bride and groom stand side by side at the chancel steps. 
Meaning of the word marked with <WSD> tags:  A hymn or other music used during a procession; prosodion.