Arise, O God - As if God were now insensible to the wrongs and sufferings of his people; as if he were inattentive and indisposed to come to their help. See the notes at Psalms 3:7.
Plead thine own cause - literally, “Contend thine own contention.” That is, Maintain a cause which is really thine own. Thine own honor is concerned; thine own law and authority are assailed; the war is really made on “thee.” This is always the true idea in the prayers which are offered for the conversion of sinners, for the establishment of truth, and for the spread of the Gospel in the world. It is not originally the cause of the church; it is the cause of God. Everything in regard to truth, to justice, to humanity, to temperance, to liberty, to religion, is the cause of God. All the assaults made on these, are assaults made on God.
Remember how the foolish man reproacheth thee daily - Constantly. He does not cease. The word “foolish” refers to the wicked. The idea is, that the wicked constantly reproach God - either by their language or their conduct; and this is a reason for calling on him to interpose. No better reason for asking his interposition can be given, than that such conduct is a real reproach to God, and reflects on his honor in the world.