There was, however, a reason for fixing on this particular number, in token of the unerring truth of the Divine Persons, Who are sometimes mentioned as two, because the Holy Ghost is the bond of the other two Persons; and sometimes as three:  as Augustine observes on John 8:17:  “In your law it is written that the testimony of two men is true.”

Reply Obj. 9:  A severe punishment is inflicted not only on account of the gravity of a fault, but also for other reasons.  First, on account of the greatness of the sin, because a greater sin, other things being equal, deserves a greater punishment.  Secondly, on account of a habitual sin, since men are not easily cured of habitual sin except by severe punishments.  Thirdly, on account of a great desire for or a great pleasure in the sin:  for men are not easily deterred from such sins unless they be severely punished.  Fourthly, on account of the facility of committing a sin and of concealing it:  for such like sins, when discovered, should be more severely punished in order to deter others from committing them.

Again, with regard to the greatness of a sin, four degrees may be observed, even in respect of one single deed.  The first is when a sin is committed unwillingly; because then, if the sin be altogether involuntary, man is altogether excused from punishment; for it is written (Deut. 22:25, seqq.) that a damsel who suffers violence in a field is not guilty of death, because “she cried, and there was no man to help her.”  But if a man sinned in any way voluntarily, and yet through weakness, as for instance when a man sins from passion, the sin is diminished:  and the punishment, according to true judgment, should be diminished also; unless perchance the common weal requires that the sin be severely punished in order to deter others from committing such sins, as stated above.  The second degree is when a man sins through ignorance:  and then he was held to be guilty to a certain extent, on account of his negligence in acquiring knowledge:  yet he was not punished by the judges but expiated his sin by sacrifices.  Hence it is written (Lev. 4:2):  “The soul that sinneth through ignorance,” etc.  This is, however, to be taken as applying to ignorance of fact; and not to ignorance of the Divine precept, which all were bound to know.  The third degree was when a man sinned from pride, i.e. through deliberate choice or malice:  and then he was punished according to the greatness of the sin [Cf.  Deut. 25:2].  The fourth degree was when a man sinned from stubbornness or obstinacy:  and then he was to be utterly cut off as a rebel and a destroyer of the commandment of the Law [Cf.  Num. 15:30, 31].