Charles H. Spurgeon on Psalms 31:13

For I have heard the slander of many. One slanderous viper is death to all comfort —what must be the venom of a whole brood? What the ear does not hear the heart does not rue; but in David's case the accusing voices were loud enough to break in upon his quiet —foul mouths had grown so bold, that they poured forth their falsehoods in the presence of their victim. Shimei was but one of a class, and his cry of "Go up, thou bloody man, "was but the common speech of thousands of the sons of Belial. All Beelzebub's pack of hounds may be in full cry against a man, and yet he may be the Lord's anointed. Fear was on every side. He was encircled with fearful suggestions, threatenings, remembrances, and forebodings; no quarter was clear from incessant attack. While they took counsel together against me, they devised to take away my life. The ungodly act in concert in their onslaughts upon the excellent of the earth: it is to be wondered at that sinners should often be better agreed than saints, and generally set about their wicked work with much more care and foresight than the righteous exhibit in holy enterprises. Observe the cruelty of a good man's foes! they will be content with nothing less than his blood —for this they plot and scheme. Better fall into the power of a lion than under the will of malicious persecutors, for the beast may spare its prey if it be fed to the full, but malice is unrelenting and cruel as a wolf. Of all fiends the most cruel is envy. How sorely was the psalmist bestead when the poisoned arrows of a thousand bows were all aimed at his life! Yet in all this his faith did not fail him, nor did his God forsake him. Here is encouragement for us.

Verses 14-18. In this section of the Psalm he renews his prayers, urging the same pleas as at first: earnest wrestlers attempt over and over again the same means of gaining their point.