For all flesh is as grass, and all the glory of man as the flower of grass. The grass withereth, and the flower thereof falleth away: But the word of the Lord endureth for ever. And this is the word which by the gospel is preached unto you. (1 Peter 1:24-25 KJV)
This says it plainly. All the accomplishments and glory man achieves will one day fade. The only thing that matters and that will endure forever is the word of God, the promises of God set forth in the Gospel.
Does this mean we should not bother trying to achieve and do well since it will all fade away? Why bother? Here is the answer to "why bother?".
Whether therefore ye eat, or drink, or whatsoever ye do, do all to the glory of God. (1 Corinthians 10:31 KJV)
Whatsoever thy hand findeth to do, do it with thy might; for there is no work, nor device, nor knowledge, nor wisdom, in the grave, whither thou goest. (Ecclesiastes 9:10 KJV)
Let us hear the conclusion of the whole matter: Fear God, and keep his commandments: for this is the whole duty of man. For God shall bring every work into judgment, with every secret thing, whether it be good, or whether it be evil. (Ecclesiastes 12:13-14 KJV)
We need to remember one thing. We work hard because God has saved us. We do not work to get God to save us.
Ultimately the only thing that lasts on this earth is the word of God. Since nothing we do from a man centered view will last we need to do all that we do with a conscience toward God for His glory. Work done with a conscience toward Him will have lasting value.
For other foundation can no man lay than that is laid, which is Jesus Christ. Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble; Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is. If any man's work abide which he hath built thereupon, he shall receive a reward. If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire. (1 Corinthians 3:11-15 KJV)