32 But neither can he be said to be in the Church, and to belong to that fellowship of the Spirit, who is mixed up with Christ's sheep by a bodily intercourse only in deceitfulness of heart. For the “Holy Spirit of discipline will flee deceit.” Wherefore whosoever are baptized in the congregations or separations rather of schismatics or heretics, although they have not been born again of the Spirit, like as it were to Ishmael, who was Abraham's son after the flesh; not like Isaac, who was his son after the Spirit, because by promise; yet when they come to the Catholic Church, and are joined to the fellowship of the Spirit which without the Church they beyond doubt had not, the washing of the flesh is not repeated in their case.
For “this form of godliness” was not wanting to them even when they were without; but there is added to them “the Unity of the Spirit in the bond of peace,” which cannot be given but within. Before they were Catholics indeed, they were as they of whom the Apostle says, “Having a form of godliness, but denying the power thereof.” For the visible form of the branch may exist even when separated from the vine; but the invisible life of the root cannot be had, but in the vine. Wherefore the bodily sacraments, which even they who are separated from the Unity of Christ's Body bear and celebrate, may give “the form of godliness;” but the invisible and spiritual power of godliness cannot in any wise be in them, just as sensation does not accompany a man's limb, when it is amputated from the body.
Source: Sermons on Selected Lessons of the New Testament (New Advent)