Adam Clarke on Psalms 102:27

But thou art the same - ואתה הוא veattah Hu, but thou art He, that is, The Eternal; and, consequently, he who only has immortality.

Thy years shall have no end - לא יתמו lo yittammu, "they shall not be completed." Every thing has its revolution - its conception, growth, perfection, decay, dissolution, and death, or corruption. It may be said that regeneration restores all these substances; and so it does in a measure, but not without deterioration. The breed of animals, as well as vegetables, wears out; but God's eternal round has no completion. I repeat it, - what is necessarily eternal is unchangeable and imperishable; all created beings are perishable and mutable, because not eternal. God alone is eternal; therefore God alone is imperishable and immutable.