The second behest is as follows: ‘Thou shalt not take God’s name in
vain;’ that is to say, ‘Thou shalt not swear for naught and without good
reason,’ which our Lord Himself forbids us in His Gospel, that one
should not swear, neither by the heaven, nor by the earth, nor by other
creature. Yet from good cause one may swear without sin, as in judgment,
where one demands oath of truth, or out of judgment from other good
cause, and with purity and reason. In no other manner is it right to
swear. And, therefore, whosoever swears without reason the name of our
Lord, and for naught, if he wittingly swears false he forswears himself,
and acts against this behest, and swears deadly, for he swears against
conscience, that is to say (understand), when he forswears himself by
thought and by long thinking. But he that swears true wittingly, and
always for naught or for some bad reason, not wickedly, but lightly and
without slander, swears venially. Nevertheless the habit is sinful, and
may well turn to deadly sin unless he beware. But he that swears
horribly by God or by His saints, and breaks him in pieces, and says
slanders about him that are not to be said, the same sins deadly. Nor
can he have reason, that he may excuse himself. And he that accustoms
himself to swear most, sins most.