Let your yea be yea; and your nay, nay

There were, we know, whole worlds of mischief at work among our Lord’s hearers and contemporaries in the matter of oaths: as first, that some were regarded as more binding than others; that those made in the name of God must indeed be performed, while of those by the altar and the gift on the altar, by the temple and the gold in the temple, some obliged, while others were of no force at all; and the spiritual rulers of the people, blind leaders of the blind, had made a scale of the obligation of these several oaths on the consciences of men (Matt. xxiii. 16-22). Then, too, men had learnt to think that if only God’s Name were avoided, there was no irreverence in the frequent oaths, ‘by heaven,’ ‘by the earth,’ ‘by Jerusalem,’ by their own heads—and in these introduced on the slightest need, or on no need whatsoever; just as now-a-days men who would not be wholly profane will substitute for the Name of God sounds that nearly resemble, but are not exactly it, or the name, it may be, of some heathen deity; and this out of a lingering respect for that Holy Name.

Richard Chenevix Trench (1807-1886), Exposition of the Sermon on the Mount, drawn from the writings of St. Augustine (4th Edition, Revised), London: Kegan Paul, Trench, & Co., 1886, pp. 217-218.