Real Communion

Unde nec illi in perditis et damnabilibus moribus debent esse securi, qui usque in finem quidem velut in communione Ecclesiae catholicae perseverant, intuentes quod dictum est: 'Qui perseveraverit usque in finem, hic salvus erit', et per vitae iniquitatem ipsam vitae iustitiam, quod eis Christus est, deserunt, sive fornicando sive alias immunditias flagitiorum, quas nec exprimere Apostolus voluit, in suo corpore perpetrando, sive turpitudine luxuriae diffluendo sive aliquid aliud eorum agendo, de quibus ait: 'Quoniam qui talia agunt, regnum Dei non possidebunt'; ac per hoc, quicumque agunt talia, nisi in sempiterno supplicio non erunt, quia in Dei regno esse non poterunt. In his enim perseverando usque in huius vitae finem non utique dicendi sunt in Christo perseverasse usque in finem, quia in Christo perseverare est in eius fide perseverare; quae fides, ut eam definit idem Apostolus, 'per dilectionem operatur'; 'dilectio' autem, sicut ipse alibi dicit, 'malum non operatur'. Nec isti ergo dicendi sunt manducare corpus Christi, quoniam nec in membris computandi sunt Christi. Ut enim alia taceam, non possunt simul esse et membra Christi et membra meretricis. Denique ipse dicit: 'Qui manducat carnem meam et bibit sanguinem meum, in me manet, et ego in eo.' Ostendit quid sit non sacramento tenus, sed re vera corpus Christi manducare et eius sanguinem bibere; hoc est enim in Christo manere, ut in illo maneat et Christus. Sic enim hoc dixit, tamquam diceret: 'Qui non in me manet, et in quo non maneo, non se dicat aut existimet manducare corpus meum aut bibere sanguinem meum'. Non itaque manent in Christo, qui non sunt membra eius. Non sunt autem membra Christi, qui se faciunt membra meretricis, nisi malum illud paenitendo esse destiterint et ad hoc bonum reconciliatione redierint. Sanctus Augustinus Hipponensis, De Civitate Dei, Lib. XXI

So those of depraved and damnable behaviour should not be secure, though they persevere to the end in the communion of the Catholic Church, and to comfort themselves say, 'He that endures to the end shall be saved.'1 for by the iniquity of their life they have deserted that very righteousness of life which Christ is to them, whether it be by fornication, or by perpetrating in their body the other uncleanness which the Apostle would not mention, or by a dissolute luxury, or by doing any one of those things of which he says, 'They who do such things shall not inherit the kingdom of God.'2 They who do such things shall not exist anywhere but in eternal punishment, since they cannot be in the kingdom of God. While they persevere in doing such things to the very end of their lives, they cannot be said to persevere in Christ to the end, for to persevere in Him is to persevere in the faith of Him. And this faith, as the Apostle's definition of it is: 'though love worked.'3 And 'love,' as he elsewhere says, 'does not work evil.'4  Nor can these be said to eat the body of Christ, for they cannot even be numbered among the members of Christ. Even passing over other things, they cannot be at once the members of Christ and the members of a whore. He Himself, when He says, 'He that eats my flesh and drinks my blood, remains in me, and I in him,'5 shows what it is in reality, and not sacramentally, to eat His body and drink His blood; for this is to remain in Christ, that He also in us might remain. So that it is as if He had said: He who does not remain in me and in whom I do not remain, let him not say or think that he eats my body or drinks my blood.' Therefore, they who are not Christ's members do not remain in Him. And they are not members of Christ who have made themselves members of a whore, unless they have penitently abandoned that evil, and have returned to this good to be reconciled to it. Saint Augustine of Hippo, from The City of God, Book 21 1 Mt 24.13 2. Gal 5.21  3. Gal 5.6  4 Rom 13.10  5 Jo. 6.57