2 With this scene of disaster and misery before Us, Our heart is heavy with the weight of bitter sorrow and We cannot but feel compelled, by reason of the charge of universal fatherhood which God has laid upon Us, not only to entreat the nations one and all to have done with rancor and make peace once more as friends, but also to urge all Our children in Christ to storm heaven with more fervent prayers, never forgetting that all efforts are inadequate and unavailing if God's good pleasure is not first obtained, according to the inspired words of the Psalmist: "unless the Lord build the house, they labor in vain that build it."
Source: Optatissima Pax (Vatican.va)