26 Is there not perchance, Venerable Brethren, in this spirit of penance also a sweet mystery of peace? "There is no peace to the wicked" ( Is. Iviii. 22), says the Holy Spirit, because they live in continuous struggle and conflict with the order established by nature and by its Creator. Only when this order is restored, when all peoples faithfully and spontaneously recognize and profess it, when the internal conditions of peoples and their outward relations with other nations are founded on this basis, then only will stable peace be possible on earth. But to create this atmosphere of lasting peace, neither peace treaties, nor the most solemn pacts, nor international meetings or conferences, nor even the noblest and most disinterested efforts of any statesman, will be enough, unless in the first place are recognized the sacred rights of natural and divine law. No leader in public economy, no power of organization will ever be able to bring social conditions to a peaceful solution, unless first in the very field of economics there triumphs moral law based on God and conscience. This is the underlying value of every value in the political life as well as in the economic life of nations; this is the soundest "rate of exchange." If it is kept steady, all the rest will be stable, being guaranteed by the immutable and eternal law of God.
Source: Caritate Christi Compulsi (Vatican.va)