Psalms 71:18

Now also when I am old and grey-headed - Margin, “unto old age and grey hairs.” This does not necessarily mean that he was then actually old and grey-headed, but it would imply that he was approaching that period, or that he had it in prospect. The time of youth was past, and he was approaching old age. The literal rendering would be, “And also unto old age and grey hairs, do not forsake me.” This is the prayer of one who had been favored in youth, and in all his former course of life, and who now asked that God would continue his mercy, and not forsake him when the infirmities of age drew on.

Forsake me not - Still keep me alive. Give me health, and strength, and ability to set forth thy praise, and to make known thy truth. See the notes at Psalms 71:9.

Until I have showed thy strength - Margin, as in Hebrew, “thine arm.” The arm is the instrument by which we execute a purpose, and it thus becomes a symbol of strength.

Unto this generation - literally, “to a generation.” The reference is to the generation then living; that is, the generation which had come on the stage since he had reached manhood - the generation - the new generation - which one who is approaching old age sees engaged in the active scenes of life, cultivating the fields, filling the offices, constructing the bridges and roads, manning the ships, occupying the dwellings, instead of those with whom he was formerly associated, and who are now in their graves. His own generation - the companions of his own early years - had passed away. He had lived to speak to a new generation, and he was desirous that they should start on the journey of life with the advantage of his experience, as of one that had gone before. Each generation “may” thus enter on life with all the accumulated wisdom of the past; that is, as wise as those had become who had themselves had the experience, and treasured up results from the observations, of a long life.

Society thus makes progress. One generation becomes wiser and better than the one which went before it, and the experience of all ages thus accumulates as the world advances, enabling a future age to act on the results of all the wisdom of the past. Man thus differs from the inferior creation. The animals, governed by instinct alone, make no progress. Compare the notes at Psalms 49:13. They profit neither by the wisdom, nor the follies of the past. The first robin built its nest of the same materials, and with as much art, as the robin does now; the first stock of bees constructed their cells with as nice and accurate adaptations, with mathematical precision as complete, as a swarm of bees will do now. Neither the bird nor the bee has learned anything by experience, by study, or by observation - nor lays up, to transmit to future generations of birds or bees, the results of its own sagacity or observation.

Not so with man. The result of the experiences of one generation goes into the general experience of the world, and becomes its capital; a new thought, or a new invention struck out by some splendid genius, becomes the common property of the race; and society, as it rolls on, gathers up all these results, as the Ganges or the Mississippi, rolling on to the ocean, gathers into one mighty volume all the waters that flow in a thousand streams, and all that come from rivulets and fountains, however remote. It is this which makes the life of “a man” so valuable in this world; this which makes it so desirable for a man, even when approaching old age, yet to live a little longer, for, as the fruit of his experience, his observation, his ripe wisdom, his acquired knowledge, he may yet suggest something, by writing or otherwise, which may add to the intelligence of the world; some principle which may be elaborated and perfected by the coming age.

And thy power - Thy greatness; majesty; glory.

To every one that is to come - To all future generations. That I may state truths which may benefit future ages. He who suggests one truth which the world was not in possession of before, is a benefactor to mankind, and will not have lived in vain, for that truth will do something to set the race forward, and to make the world better and happier. It is not a vain thing, then, for a man to live; and every one should endeavor “so” to live that the world may not be the worse - or may not go backward - by his living in it, but that it may be the wiser and the better: not merely so that it may keep on the same level, but that it may rise to a higher level, and start off on a new career.