From the Word
6 Have no anxiety about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. 7 And the peace of God, which passes all understanding, will keep your hearts and your minds in Christ Jesus.
Philippians 4:6–7, RSV
This is the true peace that satisfies and quiets the heart; not in times when no adversity is at hand, but in the midst of it, when outwardly there is nothing but strife. This is the difference between worldly and spiritual peace. Worldly peace consists in removing the outward evil that disturbs the peace; when enemies besiege a city there is no peace; but when they depart peace returns. Such is the case in poverty and sickness. While they afflict you, you are discontented; but when they are removed and there is health and plenty, there is peace and rest again. He who experiences this peace is not changed, being just as faint-hearted whether the evil be present or not; only he feels it and is frightened when it is present.
Christian or spiritual peace, however, just turns the thing about, so that outwardly the evil remains, as enemies, sickness, poverty, sin, death and the devil. These are there and never desist, encompassing us on every side; nevertheless, within there is peace, strength and comfort in the heart, so that the heart cares for no evil, is really bolder and more joyful in its presence than in its absence. Therefore it is peace which passeth and transcendeth all understanding and all the senses. Reason cannot grasp any peace except worldly or external peace; it knows not how to comfort or satisfy a person in times of affliction. But when the Spirit comes, he lets the outward adversity remain, but strengthens the person, making the timid fearless, changing the troubled into a quiet, peaceful conscience.
Whence does he receive this? From his faith in Christ. For if I truly believe in the Lord from the depth of my heart, so that it can truly say: My Lord Christ has by his resurrection conquered my need, my sin, death and all evil, and will be with and in me; it is impossible for me to be faint-hearted and timid, no matter how much sin and death oppress me. If you look to Christ and believe on him, no evil that may befall you is so great that it can harm you and cause you to despair. Therefore it is impossible for the fruit of peace to be absent where faith is.
Luther, Martin, and John Sander. Devotional Readings from Luther’s Works for Every Day of the Year. Augustana Book Concern, 1915, pp. 294–95.