Albert Barnes Commentary Psalms 119:90

"Thy faithfulness is unto all generations: Thou hast established the earth, and it abideth." — Psalms 119:90 (ASV)

Your faithfulness – The accomplishment of your promises.

Is to all generations – Margin, “to generation and generation.” From one generation to another. The generations of people change and pass away, but your promises do not change. They are as applicable to one generation as to another; they meet every generation alike. The people of no one age can lay any exclusive claim to them, or feel that they were made only for them. They are as universal – as much adapted to the new generations that come upon the earth – as the light of the sun, ever-enduring, is; or as the fountains and streams, which flow from age to age.

You have established the earth, and it abides – Margin, “Standeth.” It is firm. The earth thus established or made firm, is an illustration of your faithfulness, and of the stability and permanence of your promises. It is the same from generation to generation, with its rivers, streams, and fountains; with its fruits and flowers; with its balmy air and its sweet prospects; with its riches of gold and silver; with its pearls and diamonds; with its treasures of land and ocean. So is the word of God – so are the gracious promises which he has addressed to people – the same in every age.