I. There is a peculiarity of expression in this Psalm which we certainly should not find in any Christian hymn, and one which cannot fail to strike us. What can be more remarkable than the contrast between the former part of the text and the sublime meditation which precedes? It startles us thus to be carried from thoughts of God's omniscience and omnipresence and His superintending providence and watchful love into the midst of a conflict in which human passions are roused, to find their vent in strong invective. It is impossible to disguise the fact that there does run through the Psalter this spirit of intense hatred of wickedness and wicked men. In many instances, no doubt, the sense of wrong, and violence, and persecution stirs it into keener life. The psalmists are always in the minority, always on the weak side, humanly speaking. But they are profoundly convinced that their cause is right. They are sure that God is on their side. They hate evil with all their hearts, because they love God with all their hearts.
II. But now the question forces itself upon us, Are we justified ourselves in using these bitter and burning words? Is it right to pray, "Oh that Thou wouldest slay the wicked, O God"? Are these words in harmony with the Christian conscience? (1) It is quite plain that the general current of the Psalter, the strain and tone of feeling running through it, cannot be antagonistic to our Christian conscience, or the Christian Church throughout the world would not have adopted the Psalter as its perpetual book of devotion. Therefore, though there may be single expressions in the Psalter, imprecations and burning words, which are not suitable in Christian mouths, depend upon it that the whole strain of the Psalter, as sternly set against evil, is not opposed to the Christian conscience. (2) The New Testament is not so entirely opposed to the spirit and teaching of the Old on this point as is sometimes asserted. The chief difference lies here: (a) that in the New Testament we are taught to carry the endurance of wrong much further than was possible or conceivable before Jesus our Master set us an example that we should follow in His steps, and (b) that we are taught by Him and His Apostles what we are not taught distinctly by psalmists and prophets: to distinguish between the sinner and the sin, between the wickedness which a man does and the man himself; that we are to try and root out wickedness without rooting out the wicked from the earth; that, with the patience of God, we are to bear with the evil and seek to reform the evil, even whilst we long to see it come to an end. (3) We may not cherish a personal hatred; we may not seek for a personal vengeance. But it is our bounden duty to hate wickedness and wicked characters with all our hearts.
J. J. S. Perowne, Sermons,p. 68.