In the following passages there are references to being soldiers of Jesus Christ. Paul regarded himself as such a soldier (refers to Epaphroditus and Timothy as fellow soldiers).
Greek word for soldier: http://www.searchgodsword.org/lex/grk/view.cgi?number=4757
strat-ee-o'-tace
King James Version
Thou therefore, my son, be strong in the grac
e that is in Christ Jesus. 2And the things that thou hast heard of me among many witnesses, the same commit thou to faithful men, who shall be able to teach others also. 3Thou therefore endure hardness, as a good soldier of Jesus Christ.
Philippians 2:19-30
Yet I supposed it necessary to send to you Epaphroditus, my brother, and companion in labour, and fellow soldier, but your messenger, and he that ministered to my wants. For he longed after you all, and was full of heaviness, because that ye had heard that he had been sick. For indeed he was sick nigh unto death: but God had mercy on him; and not on him only, but on me also, lest I should have sorrow upon sorrow. I sent him therefore the more carefully, that, when ye see him again, ye may rejoice, and that I may be the less sorrowful. Receive him therefore in the Lord with all gladness; and hold such in reputation: Because for the work of Christ he was nigh unto death, not regarding his life, to supply your lack of service toward me."
“Suffer hardship with me, as a good soldier of Christ Jesus. No soldier in active service entangles himself in the affairs of everyday life, so that he may please the one who enlisted him as a soldier.”
(2 Timothy 2:3-4)