In Dracula, what's a missal?

A missal is a large book that contains the prayers, readings, and instructions authorized by the Roman Catholic Church, and used by priests for the celebration of Mass. The word also refers to the small book that a person uses while attending Mass.

In a gripping scene from Bram Stoker's Dracula, Arthur drives a stake through the heart of his beloved Lucy, who has become one of the Un-Dead:

Arthur took the stake and the hammer, and when once his mind was set on action his hands never trembled nor even quivered. Van Helsing opened his missal and began to read, and Quincey and I followed as well as we could.

Arthur placed the point over the heart, and as I looked I could see its dint in the white flesh. Then he struck with all his might.

The thing in the coffin writhed, and a hideous, blood-curdling screech came from the opened red lips. The body shook and quivered and twisted in wild contortions. The sharp white teeth champed together till the lips were cut, and the mouth was smeared with a crimson foam.