Besides the references to grass as literal food for animals, the Scriptures use grass also as simile for human finitude and impermanence. For example:
15 As for man, his days are like grass; he flourishes like a flower of the field;
16 for the wind passes over it, and it is gone, and its place knows it no more.
17 But the steadfast love of the LORD is from everlasting to everlasting on those who fear him, and his righteousness to children's children, (Ps. 103:15-17 ESV)
The Scriptures remind us in many ways that we are not here for very long before we're gone. This is just what we need, since we are prone to forget that our time is limited, and our efforts are not all we'd like to think they are.
Let us consider a model in which each generation lives 90 years and in which each generation begins to have children at age 30. A lifetime of 90 years is generous but not absurd. The use of 30 as an age-marker for having children is not unreasonable in our society, though it occurred much earlier in previous times.
Let us say someone, call him or her Person 0, lives from years 0 to 90, where year 0 is the birthday of that person. His/her children live from years 30 to 120, the grandchildren live from years 60 to 150, and the great-grandchildren live from years 90 to 180. Notice that the great-grandchildren have no living memory of Person 0. All knowledge of Person 0 will necessarily be second-hand, via oral communication or by various media.
The amount of information and personal knowledge of Person 0 passed down through each generation also gets progressively smaller. That is, the children have direct experience and knowledge of Person 0; the grandchildren will also have direct experience and knowledge of Person 0, but there is less of it; it is at one level of indirection, if you will. The great-grandchildren will have knowledge but no direct experience, as noted, of Person 0; furthermore, the amount of knowledge of Person 0 will also be attenuated. For the great-great-grandchildren, the attenuation is even more pronounced, and the amount of any knowledge of Person 0 goes rapidly to zero.
That is, if you are generation 0, then your great-grandchildren (generation 3) will have no living memory of you and greatly attenuated knowledge about you, and at generation 4, the knowledge about you will likely be close to zero. This means that knowledge of what you have done and what you were like is gone.
Society does not remember people unless they do something very good or very bad. Most of us do not fit into either category, therefore, society will not remember us after a point. As noted, our descendants will likely not remember us either after four generations.
All of us take pride and pleasure in various accomplishments in our lives. Yet, in all likelihood, the particulars of our works will never be known past a certain point in time. No one will know or care, even if written or electronic records survive about us.
Where does this leave us?
It leaves us in despair and insignificance were it not for the fact that God sees all and remembers all. This is not in reference to his judgment of our sins and iniquities, but rather to the fact that all the details of our lives, who we were and what we did, are alive and known forever by God. God does not forget. In particular, if you tried to serve him in the family, on the job or in the broader society, God does not forget. We remain significant in his sight, and all those things we did in his name or because he told us to, are precious to him and remain in his consciousness.
In case anyone is wondering, I am not suggesting that our works and good intentions save us. No, they do not. We cannot atone for our sins. We can only look to the one designated sin-bearer to atone for us, Jesus Christ the Righteous.