Chapter 4.— 5.  Further, if any one fails to understand how it can be that we assert that the sacrament is not rightly conferred among the Donatists, while we confess that it exists among them, let him observe that we also deny that it exists rightly among them, just as they deny that it exists rightly among those who quit their communion.  Let him also consider the analogy of the military mark, which, though it can both be retained, as by deserters, and, also be received by those who are not in the army, yet ought not to be either received or retained outside its ranks; and, at the same time, it is not changed or renewed when a man is enlisted or brought back to his service.  However, we must distinguish between the case of those who unwittingly join the ranks of these heretics, under the impression that they are entering the true Church of Christ, and those who know that there is no other Catholic Church save that which, according to the promise, is spread abroad throughout the whole world, and extends even to the utmost limits of the earth; which, rising amid tares, and seeking rest in the future from the weariness of offenses, says in the Book of Psalms, "From the end of the earth I cried unto Thee, while my heart was in weariness:  Thou didst exalt me on a rock." 1151   But the rock was Christ, in whom the apostle says that we are now raised up, and set together in heavenly places, though not yet actually, but only in hope. 1152   And so the psalm goes on to say, "Thou wast my guide, because Thou art become my hope, a tower of strength from the face of the enemy." 1153   By means of His promises, which are like spears and javelins stored up in a strongly fortified place, the enemy is not only guarded against, but overthrown, as he clothes his wolves in sheep’s clothing, 1154 that they may say, "Lo, here is Christ, or there;" 1155 and that they may separate many from the Catholic city which is built upon a hill, and bring them down to the isolation of their own snares, so as utterly to destroy them.  And these men, knowing this, choose to receive the baptism of Christ without the limits of the communion of the unity of Christ’s body, though they intend afterwards, with the sacrament which they have received elsewhere, to pass into that very communion.  For they propose to receive Christ’s baptism in antagonism to the Church of Christ, well knowing that it is so even on the very day on which they receive it.  And if this is a sin, who is the man that will say, Grant that for a single day I may commit sin?  For if he proposes to pass over to the Catholic Church, I would fain ask why.  What other answer can he give, but that it is ill to belong to the party of Donatus, and not to the unity of the Catholic Church?  Just so many days, then, as you commit this ill, of so many days’ sin are you going to be guilty.  And it may be said that there is greater sin in more days’ commission of it, and less in fewer; but in no wise can it be said that no sin is committed at all.  But what is the need of allowing this accursed wrong for a single day, or a single hour?  For the man who wishes this license to be granted him, might as well ask of the Church, or of God Himself, that for a single day he should be permitted to apostatize.  For there is no reason why he should fear to be an apostate for a day, if he does not shrink from being for that time a schismatic or a heretic. 1151     Ps. lxi. 2, 3 .  Cp. Hieron, and LXX. 1152     Eph. ii. 6 . 1153     Ps. lxi. 2, 3 .  Cp. Hieron, and LXX. 1154     Matt. vii. 15 . 1155     Matt. xxiv. 23 .