Matthew 5:33 - Ellicott's Commentary On The Whole Bible

By them of old time. — Read, to them of old time, as before. Here, again, the reference is to the letter of the Law as taught by the Rabbis, who did not go beyond it to its wider spirit. To them the Third Commandment was simply a prohibition of perjury, as the Sixth was of murder, or the Seventh of adultery. They did not see that the holy name (Leviticus 19:12) might be profaned in other ways, even when it was not uttered; and they expressly or tacitly allowed (See Philo, De Special. Legg.) many forms of oath in which it was not named, as with the view of guarding it from desecration. Lastly, out of the many forms thus sanctioned (as here and in Matthew 23:16-22) they selected some as binding, and others as not binding, and thus by a casuistry at once subtle, irrational, and dishonest, tampered with men’s sense of truthfulness.