Schopenhauer quite rightly notes that all is impermanent and all will decay. His solution is to reject all hope and expectation and thus avoid disappointment. As we have seen from Shakespeare and Shelley, this is not the only potential response. One could bemoan the tragedy of loss (Macbeth), receive the knowledge with equanimity (Tempest), or realize there will be loss and thus hold more tightly to and cherish what is good knowing that it will all soon be lost (Shakespeare & Shelley).
Another response is the redemption of all that is lost. The book of Ecclesiastes famously declares, “Vanity of vanities, all is vanity”. Eccl. 1:2 Vanity translates a Hebrew word Hebel, which refers to something which is transient, insubstantial, like a breath or mist. From that, the writer draws the conclusion that nothing is world is sufficient to bring contentment to anyone in this life:
Ecclesiastes 2:10–11 (ESV)
10 And whatever my eyes desired I did not keep from them. I kept my heart from no pleasure, for my heart found pleasure in all my toil, and this was my reward for all my toil. 11 Then I considered all that my hands had done and the toil I had expended in doing it, and behold, all was vanity and a striving after wind, and there was nothing to be gained under the sun.
That however does not end the matter:
Ecclesiastes 12:13–14 (ESV)
13 The end of the matter; all has been heard. Fear God and keep his commandments, for this is the whole duty of man. 14 For God will bring every deed into judgment, with every secret thing, whether good or evil.
That matter of bringing everything into judgment may sound ominous. However, what it means in the context of the world being temporal is that the world is also meaningful: There will be a date on which all things which be confirmed as having eternal significance. The solution to the temporality of the world is not renounce the world and all its good; nor is it to love in despair. Rather, knowing that the temporal world will be judged and remade as a permanent matter will make this world and life meaningful.
In the 15th chapter of his first letter to the Corinthian church Paul lays out the Christian doctrine of the resurrection, wherein even the human body will not be lost but will be remade in an unchanging manner:
1 Corinthians 15:42 (ESV)
42 So is it with the resurrection of the dead. What is sown is perishable; what is raised is imperishable.
In light of the resurrection, our life and work is not meaningless:
1 Corinthians 15:58 (ESV)
58 Therefore, my beloved brothers, be steadfast, immovable, always abounding in the work of the Lord, knowing that in the Lord your labor is not in vain.
By stating their labor is not in vain, Paul is underscoring the permanence of human existence. The mutability of the world is not the last word. The Christian sees the world as temporal, along with the Buddhist, but rather than seeing the end as dissolution, sees the end as permanence:
2 Corinthians 4:16–18 (ESV)
16 So we do not lose heart. Though our outer self is wasting away, our inner self is being renewed day by day. 17 For this light momentary affliction is preparing for us an eternal weight of glory beyond all comparison, 18 as we look not to the things that are seen but to the things that are unseen. For the things that are seen are transient, but the things that are unseen are eternal.
Therefore, happiness is not contingent upon renunciation, nor must one “cross-fingers”, and know that the joy will be destroyed. Rather, the goal is set hope upon permanent joys.