Concise Bible Dictionary:
Apart from the common application of this term (for which see ARMY, Armor, &c.) it is used in the New Testament for the service of a Christian. Two things are said of the Christian soldier. He must “endure hardness,” that is, share in the suffering incident to warfare; and he must not entangle “himself with the affairs of this life, that he may please him who hath chosen him to be a soldier”; that is, be quite free to obey his Captain in all things. As explained by the centurion, “I say to this man Go, and he goeth; and to another, Come, and he cometh;” so the Christian servant is under authority, and unhesitating obedience is what should characterize the soldier of Jesus Christ: he must be prepared to endure hardships, and to suffer with his Captain (Matt. 8:9; 2 Tim. 2:3-4).