Charles H. Spurgeon on Psalms 71:15

My mouth shall shew forth thy righteousness and thy salvation all the day. We are to bear testimony as experience enables us, and not withhold from others that which we have tasted and handled. The faithfulness of God in saving us, in delivering us out of the hand of our enemies, and in fulfilling his promises, is to be everywhere proclaimed by those who have proved it in their own history. How gloriously conspicuous is righteousness in the divine plan of redemption! It should be the theme of constant discourse. The devil rages against the substitutionary sacrifice, and errorists of every form make this the main point of their attack; be it ours, therefore, to love the doctrine, and to spread its glad tidings on every side, and at all times. Mouths are never so usefully employed as in recounting the righteousness of God revealed in the salvation of believers in Jesus. The preacher who should be confined to this one theme would never need seek another: it is the medulla theologae, the very pith and marrow of revealed truth. Has our reader been silent upon this choice subject? Let us, then, press him to tell abroad what he enjoys within: he does not well who keeps such glad tidings to himself. For I know not the numbers thereof. He knew the sweetness of it, the sureness, the glory, and the truth of it; but as to the full reckoning of its plenitude, variety, and sufficiency, he felt he could not reach to the height of the great argument. Lord, where I cannot count I will believe, and when a truth surpasses numeration I will take to admiration. When David spoke of his enemies, he said they were more in number than the hairs of his head; he had, therefore, some idea of their number, and found a figure suitable to set it out; but, in the case of the Lord's covenant mercies, he declares, "I know not the number, "and does not venture upon any sort of comparison. To creatures belong number and limit, to God and his grace there is neither. We may, therefore, continue to tell out his great salvation all day long, for the theme is utterly inexhaustible.