But now inquiry is being made concerning these issues. First, can any believer enlist in the military? Second, can any soldier, even those of the rank and file or lesser grades who neither engage in pagan sacrifices nor capital punishment, be admitted into the church? No on both counts.
TertullianThus the connection of the Father in the Son, and of the Son in the Paraclete, produces three coherent Persons, who are yet distinct One from Another. These three are one [thing], not one [Person], as it is said, 'I and my Father are One,' in respect of unity of substance not singularity of number.
Tertullian