When our Lord descended from the Mount of Transfiguration with Peter, James and John, He was confronted by a man who complained that the disciples who had remained below had been unable to cast out the demon from his lunatic (lit., "moonstruck") son. After Jesus had rebuked the demon and it came out, the disciples asked him why they had been unable to do likewise, and our Lord replied that it was because of their lack of faith. He then goes on to say, "If you have faith as a mustard seed, you will say to this mountain, 'move from here to there,' and it will move; and nothing will be impossible for you. Howbeit, this kind does not go out save by prayer and fasting." It was, then, due to the weakness of their faith that the disciples were incapable of casting out the demon. Even so, evil can become so entrenched that even our most fervent faith is not sufficient to uproot it.
And so, as the Apostle Timothy writes, "be strong in the grace that is in Christ Jesus.... Ye therefore must endure hardship as a good soldier of Jesus Christ, remembering that no one engaged in warfare entangles himself in the affairs of this life." Now as baptized Orthodox Christians, we have all been enrolled in the Militia of Christ, empowered by the Holy Spirit to engage in spiritual warfare against the principalities and powers that rule this fallen world and who ever seek to destroy all who remain steadfast in the Faith--in the sure hope that all who endure unto the end shall be saved.
To be sure, not all of us are qualified to be front line soldiers. Most of us are called to serve in some capacity behind the lines--according to the measure of grace God has bestowed upon us--supporting those who bear the brunt of the battle. But whatever our name, rank and serial number, we are obligated by our terms of service to undergo regular training and discipline--even in times of relative peace. A good soldier will never let down his guard, but remains ever vigilant and prepared for battle, lest the Adversary should attack unexpectedly and find the soldier unprepared for combat.
Now if this be true for a warrior who serves an earthly king, how much more so for a warrior who serves the King of king--not for the sake of worldly glory and honor, but rather that he may be made worthy of the eternal glory of God's heavenly Kingdom? It is for this reason that every Orthodox Christian, of whatever rank, is called to live an ascetic life of prayer, fasting, spiritual reading and meditation, and regular participation in the Holy Mysteries of the Church, striving to acquire the virtues while living a life of sacrificial love. Only thus can we hope to receive a crown of victory on that dreadful Day when our Lord, God and Savior Jesus Christ shall return to judge both the living and the dead.