In Ecclesiastes 9:1-2 the Preacher says, "The righteous and the wise and their works are in the hand of God, and man does not know if he is worthy of love or hatred, but all things are kept uncertain in the future."
The works of man are uncertain. We labour and toil, but we do not know if God is pleased with what we do simply based on our works. Whether you are faithful or faithless, things turn out equally here on earth. The godless man gets promoted. The godly man gets promoted. Trusting in our works is futile and will lead us to despair.
However, God has made it this way on purpose. He does not want us to look to ourselves and what we have done, but to Him. His Word is certain. His Word has declared the present and the future. We know how He feels towards us because He tells us in His Word. He promises us the benefits of His Son, that His death and resurrection are ours by faith. By faith we know that God is pleased with us, that He is pleased with our works, that He has prepared rewards for us in heaven that cannot be compared with any earthly gains.
Our certainty rests in God. Our righteousness rests in God. Our life and very being rests in God. Let us let it rest in Him. Let us hold onto Him and all that He does for us and forgo all else. He has declared what will be. And His Word is certain.