How do texts advocate values that transcend temporal and spatial boundaries?

Shakespeare's plays do tend to have a timeless quality to them, as can be seen by their enduring presence in dramatic circles, all the way to the present. They've often had their settings updated to fit different time periods, including contemporary society, and this is not by accident. Shakespeare does tend to focus heavily on characterization, and universal themes of the human condition, and for all that society has changed over the centuries since Shakespeare's day, people remain people, with many of the same concerns and shared experiences.
We see this in the example of Twelfth Night, which tackles several universal themes. It is ultimately a story about love (as well as longing), but that theme extends beyond the realm of romantic love. We see bonds of friendship, between Antonio and Sebastian, to such a point that Antonio will risk his own safety, following Sebastian into Illyria, where he is surrounded by enemies. We can observe its plot of mistaken identities, with Viola impersonating a man in order to enter the inner circle of the Duke. It depicts romantic frustration, with Viola pining after Orsino, Orsino pining after Olivia, and Olivia pining after the disguised Viola, as well as the internalized conflict this situation creates, with Viola torn between her duty and loyalty to the Duke, and her own romantic desires. In these sorts of qualities, Twelfth Night presents a vivid depiction of humanity, and in this it transcends any particular time period and culture, including the one in which it was created.

I think this question is trying to insinuate that works like those of Shakespeare can stand the test of time because they convey universal, lasting messages about the nature of existence.
So, to answer this question within the context of Twelfth Night, it’s important to select a thematic idea. One of the most important thematic ideas in the play is the nature of love. A major question addressed in Viola’s devotion to Orsino is this: if you truly love someone, does it matter if he or she loves you in return?
Viola, in disguise as her brother Sebastian, tries her absolute best to kindle Orsino’s relationship with Olivia, the woman that Orsino has been wooing when Viola arrives. She is willing to put aside her personal feelings in order to make Orsino happy. Despite the fact that the play was written in the 17th century, written by a British author, and set in Illyria, its message about the selflessness of love is an enduring one.
Therefore, literature transcends its time period and cultural origin because of the themes an author can communicate through a text.