From the preview:
The Deacon is not only capable to defending his brothers against the physical assaults of the enemy, but also the emotional and psychological effects of battle. Some of his tools may be designed by chemists and researchers, but others come directly from the Deacon himself. Candidates for this particular role are always preachers first and foremost, and are selected chiefly for their ability to rouse the emotions of their congregations. Those who have shown a knack for kindling the fires of zeal in their followers and goading those into outright passion are the ones chosen to test their suitability for the commission. Not every rousing orator is destined to be a Deacon however, for the requirements are as varied as they are stringent. Although their battlefield sermons must have the power to rally troops against the emotional abuse of Skarrd psychogenics as well as the sheer horror of slaughter, they must also be able identify a variety of threats in the heat of conflict, to efficiently hurl the vials of holy Sacraments to counteract them, and in times of need, to wield the Reckoner grenade launcher with which each Deacon is armed. It is a rare individual, indeed, who is capable of all these things, and the ranks of the Deacons are not overflowing.