Psalms 71:9

My hope from my youth, "cast me not away in time of old age" [Psalm 71:9]. What is this time of old age? "When my strength shall fail, forsake not me." Here God makes this answer to you, yea indeed let your strength fail, in order that in you mine may abide: in order that you may say with the Apostle, "When I am made weak, then I am mighty." [2 Corinthians 12:10] Fear not, that you be cast away in that weakness, in that old age. But why? Was not your Lord made weak on the Cross? Did not most mighty men and fat bulls before Him, as though a man of no strength, made captive and oppressed, shake the head and say, "If Son of God He is, let Him come down from the Cross"? Has he deserted because He was made weak, who preferred not to come down from the Cross, lest He should seem not to have displayed power, but to have yielded to them reviling? What did He hanging teach you, that would not come down, but patience amid men reviling, but that you should be strong in your God? Perchance too in His person was said, "As it were a monster I have become unto many, and You are a strong Helper." In His person according to His weakness, not according to His power; according to that whereby He had transformed us into Himself, not according to that wherein He had Himself come down. For He became a monster unto many. And perchance the same was the old age of Him; because on account of its oldness it is not improperly called old age, and the Apostle says, "Our old man has been crucified together with Him." [Romans 6:6] If there was there our old man, old age was there; because old, old age. Nevertheless, because a true saying is, "Renewed as an eagle's shall be Your youth;" He rose Himself the third day, promised a resurrection at the end of the world. Already there has gone before the Head, the members are to follow. […]

Cast me not off in the time of old age,....

But it intimates that he had reason to hope God would not desert him; the faithful servants of God may be comfortably assured that he will not cast them off in old age, nor forsake them when their strength fails them. He is a Master that is not wont to cast off old servants.

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!

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. Forsake me not when my strength faileth. Bear with me, and endure my infirmities. To be forsaken of God is the worst of all conceivable ills, and if the believer can be but clear of that grievous fear, he is happy: no saintly heart need be under any apprehension upon this point.