Albert Barnes Commentary Psalms 37:18

"Jehovah knoweth the days of the perfect; And their inheritance shall be for ever." — Psalms 37:18 (ASV)

The Lord knoweth the days of the upright (Psalms 37:18). See the notes at Psalm 1:6. He knows how long they will live and all that will happen to them. He sees their whole course of life; He sees the end.

It is implied here that His eyes are on all the allotted days of their life, on all that has been ordained for them in the whole course of their life, and that nothing can shorten the days appointed to them.

The wicked expect to live, hope to live, and make their arrangements to live; but their eyes cannot rest on the future, and they cannot see the end—cannot tell precisely when they will be cut off. Some unexpected calamity—something which they cannot foresee—may come upon them and cut short their days long before the expected time; but this cannot happen in respect to Him whose eyes are on the righteous.

Nothing can prevent their reaching the end which He has fixed as the termination of their lives.

And their inheritance shall be forever (Psalms 37:18). This inheritance shall be permanent, enduring.

Perhaps all that was implied in this language, as it was used by the psalmist, was that they would continue, or would not be cut off as the wicked are; that is, that righteousness would contribute to length of days upon the earth .

Yet the language suggests a higher idea and is applicable to the righteous in respect to the promise that they will be put in everlasting possession of that which they inherit from God; that is, that they will be literally blessed forever. They will have a sure inheritance on earth, and it will endure to all eternity in another world.