Psalms 61:3

For that Church is founded on a rock, as the Lord says, "Upon this rock I will build my Church." But they build on the sand, as the same Lord says, "Every one that heareth these sayings of mine, and doeth them not, shall be likened unto a foolish man, which built his house upon the sand." But that you may not suppose that the Church which is upon a rock is in one part only of the earth, and does not extend even to its furthest boundaries, hear her voice groaning from the psalm, amid the evils of her pilgrimage. For she says, "From the end of the earth have I cried unto Thee; when my heart was distressed Thou didst lift me up upon the rock; Thou hast led me, Thou, my hope, hast become a tower of courage from the face of the enemy." See how she cries from the end of the earth. She is not therefore in Africa alone, nor only among the Africans, who send a bishop from Africa to Rome to a few Montenses, and into Spain to the house of one lady. See how she is exalted on a rock. All, therefore, are not to be deemed to be in her which build upon the sand, that is, which hear the words of Christ and do them not, even though both among us and among you they have and transmit the sacrament of baptism. See how her hope is in God the Father, the Son, and the Holy Ghost,—not in Peter or in Paul, still less in Donatus or Petilianus.

It is clear that this obligation and condition of life includes not only those who have responded so well to sound advice that they have sold their goods and distributed them to the poor, and, with their shoulders freed of every worldly burden, bear the light yoke of Christ. They also include the weaker soul, who is less capable of such glorious perfection but who nevertheless remembers that he is a Christian when he hears that he must give up Christ or lose all his possessions. He will rather lay hold on the "tower of strength against the face of the enemy" because, when he was building it by his faith, he took into account the charges with which it could be completed. He embraced the faith with the intention of renouncing this world, not in word only, because, if he bought something he was as one not possessing it, and if he used this world he was as one not using it, not placing his hope in the uncertainty of riches but in the living God.

We should note that this flood of temptations assails the church in three ways: "one is tempted, drawn on and lured by one's own desire," or is worn down by the depravity of false brothers or is assaulted by the more open snares of those …

For thou hast been a shelter for me,....

"Thou hast been my strong tower from the enemy, and thou art as strong a ever, and thy name is as much a refuge to the righteous as ever it was." Prov. xviii.