The adjutant to the pastor, also known as the armor-bearer, serves his pastor or leader in any way possible. He acts as a spiritual equivalent to a personal assistant, most commonly serving in Protestant churches. Generally, because of the personal issues involved, women usually serve women, and men usually serve men. The job description of an adjutant can vary as much as the leader desires.
An armor-bearer's most obvious responsibility, as suggested by the title, is helping a warrior carry their weapons into a battle. Although there are a handful of armor-bearers in the Bible, there's no consistent or clear job description.
Long before David was a king, he was an armor-bearer for King Saul.