Verse 9. "Cast me not off in the time of old age …" David was not tired of his master, and his only fear was lest his master should be tired of him. The Amalekite in the Bible history left his Egyptian servant to famish when he grew old and sick, but not so the Lord of saints. Even to hoar hairs He bears and carries us. Alas for us, if we were abandoned by our God, as many a courtier has been by his prince! Old age robs us of personal beauty, and deprives us of strength for active service; but it does not lower us in the love and favour of God. An ungrateful country leaves its worn-out defenders to starve upon a scanty pittance, but the pensioners of heaven are satisfied with good things.
Verse 14. "But I will hope continually, and I will yet praise thee more and more." Christian! Every day swells the tide of your mercies, adds to your heap, increases your treasure, and heightens your stature. Therefore, as the coat thou didst wear as a child, would not become thee now thou art a man, neither will the "garment of praise" with which thou didst clothe thyself when a young convert, become thee now when thou art an old disciple. Thou standest deeper in God's books than ever before, and God expects according to what every man received. You would not rent a farm now at the same rate that it bore fifty years ago. And why then may not God raise the rent of His mercies to you?
Verse 17. "O God, thou hast taught me from my youth …" God taught David by his shepherd's crook, and by the rod and sceptre of a king He also taught him. He taught him by the shouts of the multitude – "Saul hath slain his thousands, but David his tens of thousands" – and He taught him just as much, if not more, by the contempt he met within the courts of the Philistines. He taught him by the faithlessness of Abiathar, and the faithlessness of even his faithful Joab; and He taught him by the faithfulness of Abishai, and the faithfulness of Mephibosheth – and let me add, also, by the rebellion of Absalom, and the selfishness of Adonijah. They were all means by which the Lord taught His servant. And be assured, you that are under His teaching, there is nothing in your lives, but He can teach you by it. By comforts and crosses, by your wounds and your healings, by what He gives you and by what He takes away. He unteaches His child that He may teach him; shows him his folly that He may make him wise; strips him of his vain confidence, that He may give him strength; makes him know that he is nothing, that He may show him that he has all in the Lord – in Jesus His beloved.
Verse 18. "Now also when I am old and greyheaded, O God, forsake me not …" Those ships that have been in long voyages at sea, and have gone through hot climates and cold, and have run through many a difficulty and great storm, and yet have been "kept alive," as they say – when they meet one another, how many greetings pass between them? And old disciples should do likewise, because God has kept grace alive in their souls. I would ask you, how many ships have you seen cast away before your eyes? How many that have made "Shipwreck of faith and a good conscience," as the apostle speaks? This and that profession that has run into this and that error damnable, or false opinions and teaching; others that have struck upon quicksands of worldly preferments, and may split upon rocks, and yet, you have been kept. This should move you to bless this your God, the God of all grace.
Verse 20. "Thou, which hast showed me great and sore troubles, shalt quicken me again …" The number of great works that have been born out of "great and sore troubles" in the history of the Church of Christ are far beyond the telling. Just over a hundred years ago, a man knelt by the grave of a departed loved one in a little cemetery sitting under the shadow of the Swiss Alps. As he plucked away the dead leaves of a rose bush, he was interrupted by the opening of the cemetery gate, and the sound of footsteps making their way towards a grave nearby. Not long afterwards, the night air was heavy with the sobs of a man's heart. They were strong, manly tears that fell on the mounds of earth over which the visitor had stretched himself, and the unperceived watcher was only too aware of the story that lay behind those tears. The man in question was the great Merle D'Aubigne – the historian of the Reformation period – and below the earth where he was prostrated in his "great and sore troubles" lay the infant bodies of four of his dear children. In the mysterious providences of God one child had died in turn as each of the four volumes of his great work had been issued, and now the fifth volume must soon appear, and there were yet two children at home. But God stayed His hand in mercy.