Charles H. Spurgeon on Psalms 55:19

Because they have no changes, etc. Or, with whom also there be no changes, yet they fear not God. If changes be referred to their temporal estates and welfare, as Job 10:17 (it is the same word there as here, twkylx), "changes and war are against me:" then, according to the first translation, because etc., a reason is given of their perseverance in wickedness, and contempt of God; to wit, their constant and uninterrupted worldly prosperity. Or, according to the second, With whom there are no changes, yet, etc.; it is a great aggravation of their impenitency, that notwithstanding so much goodness vouchsafed unto them, they should continue so unthankful as to requite so ill, or so stupid and insensible as not to acknowledge the author. But if changes be referred, as by many, to the soul, then the meaning is —that through long use and continuance of sinning, they are, through God's just judgment, become altogether obdurate and inflexible; and therefore, no wonder if nothing work upon them to their conversion. "Can the Ethiopian change his skin?" etc. Jer 13:23. But this changes might also have another meaning. The Grecians used to say, streptai esylwn, that the minds or hearts of good men are changeable; their meaning is, that good men are merciful. Quos quisque est major, magis est placabilis ira: et faciles motus mens generosa capit, as the Latin proverb expresses it. He may therefore say, that they show by their cruel unmercifulness, that they have no fear or sense of God at all; else they would fear him, of whose mercy themselves stood in so much need, and consider that they whom they so fiercely persecute are his creatures as well as they. Westminster Assembly's Annotations.