One may lay down one's life for what one believes but one may not take up arms or kill as a believer. This stance is written large into the Gospel of Mark as part and parcel of what defines one as a Christian baptized into the body and blood of Jesus. This decision and its ramification, as outlined in Mark, became the teaching and practice of the first 350 years of the church — no member of an army or anyone willing to kill can be admitted to baptism. They may be enrolled in the catechumenate but they cannot be baptized since they are lacking in the primary "mark," if you will, of a follower of Jesus — one who lives by love, even love unto death and love for enemies as friends, in imitation of Jesus, who loves all of us this way.

Megan McKenna, On Your Mark