Alarmed (4426) (pturo from ptoeo = scare: frighten; terrify) in the active voice means to frighten or to scare, but it is used more often in a passive sense which means to let oneself be intimidated, to be frightened or to be terrified. Pturo was used to describe a frightened horse shying away on the battlefield and about to stampede. Paul is saying they are not to be fearful as the result of being intimidated. Don't be afraid, scared, frightened or terrified like a horse shying in battle. Don't be startled. Present tense calls for this to be our continual attitude. Diodorus Siculus, speaking of chariot-horses of Darius at battle of Issus Frightened (pturomenoi) by reason of the multitude of the dead heaped round them, they shook off their reins. Plutarch says The multitude is not easy to handle so that it is safe for any one to take the reins; but it should be held sufficient, if, not being scared by sight or sound, like a shy and fickle animal, it accept mastery. Barclay has a picturesque translation that you are not put into fluttering alarm Perhaps there is an allusion to Cassius who at the battle of Philippi committed suicide at the fear of defeat. In any event Paul is saying that the Philippians are not to be startled, frightened or terrified like an uncontrollable stampede of horses. God wants fearless fighters with undaunted courage, who will not be startled or intimidated by anything. Such holy boldness is produced by the Holy Spirit. (see Torrey's Topic Holy Boldness)