354 THE UNITY OF THE CHURCH.
consequently of visible and invisible elements, because it harmonizes with the natural order and by God's will belongs to the very essence of the Church, must neces- sarily remain so . long as the Church itself shall endure. Wherefore Chrysostom writes: "Secede not from the Church: for nothing is stronger than the Church. Thy hope is the Church; thy salvation is the Church; thy refuge is the Church. It is higher than the heavens and wider than the earth. It never grows old, but is ever full of vigor. Wherefore holy writ pointing to its strength and stabihty calls it a mountain." ^
Also Augustine says: "Unbelievers think that the Christian religion will last for a certain period in the world and will then disappear. But it will remain as long as the sun — as long as the sun rises and sets; that is, as long as the ages of time shall roll, the Church of God — the true body of Christ on earth — will not disappear." ^ And in another place: "The Church will totter if its foundation shakes; but how can Christ be moved? . . . Christ re- maining immovable, it (the Church) shall never be^ shaken. Where are they that say tKat the Church has disappeared from the world, when it cannot even be shaken?"^
He who seeks the truth must be guided by these funda- mental principles. That is to say, that Christ the Lord instituted and formed the Church : wherefore when we are asked what its nature is, the main thing is to see what Christ wished, and what in fact He did. Judged by such a criterion it is the unity of the Church which must be prin- cipally considered; and of this, for the general good, it has seemed useful to speak in this Encyclical.
It is so evident from the clear and frequent testimonies of holy writ that the true Church of Jesus Christ is onej that no Christian can dare to deny it. But in judging and determining the nature of this unity many have erred in various ways. Not the foundation of the Church alone,
' Horn. De capt» Eutropio, n. 6. ' In Psalm. Ixx. n. 8.
^ Enarratio in Psalm, ciii., sermo ii., n. 5.
