Charles H. Spurgeon on Psalms 86:3

Be merciful unto me, O Lord. The best of men need mercy, and appeal to mercy, yea to nothing else but mercy; they need it for themselves, and crave it eagerly of their God as a personal requisite. For I cry unto thee daily. Is there not a promise that importunity shall prevail? May we not, then, plead our importunity as an argument with God? He who prays every day, and all the day, for so the word may mean, may rest assured that the Lord will hear him in the day of his need. If we cried sometimes to man, or other false confidences, we might expect to be referred to them in the hour of our calamity, but if in all former times we have looked to the Lord alone, we may be sure that he will not desert us now. See how David pleaded, first that he was poor and needy, next that he was the Lord's set apart one, then that he was God's servant and had learned to trust in the Lord, and lastly that he had been taught to pray daily; surely these are such holy pleadings as any tried believer may employ when wrestling with a prayer hearing God, and with such weapons the most trembling suppliant may hope to win the day.