In the given statement, the "to" in "what to want" serves as an infinitive marker. It is used before the base form of the verb "want" to form an infinitive phrase. The infinitive phrase "to want" acts as the direct object of the verb "know."
Let's break down the sentence to understand its meaning:
"We can never know what to want because, living only one life, we can neither compare it with our previous lives nor perfect it in our lives to come."
In this context, "to want" refers to the things or desires we are supposed to or should want in life. However, the author argues that we can never fully know what these desires are because of certain limitations:
"Living only one life" implies that we don't have the experience of multiple lives to compare and understand what we truly want or need. Without having experienced different lives, we lack a reference point for comparison.
"We can neither compare it with our previous lives nor perfect it in our lives to come." Since we have only one life and cannot experience potential future lives, we cannot know if our desires in this current life are the best or most suitable ones. Additionally, as we don't have the opportunity for multiple lives, we cannot perfect or improve our desires through subsequent experiences.
Therefore, the idea expressed here is that due to our limited experience of one life, we cannot have a definitive understanding of what we should want or desire, leading to uncertainty and introspection about our life choices and aspirations.