If we take the idea that art is itself fleeting but that it can access the unconscious or the eternal, how can we apply this to the works of Arthur Rimbaud? I feel like it is because his art is symbolic and accesses truth that way and language is fleeting but I am not entirely sure.
Most people would agree that art is enduring and can define the artist long after he or she has personally been forgotten. For those experiencing art, there is a fleeting glimpse into someone else's understanding of his or her surroundings and his or her interpretation of whatever is being defined in that artwork, be it painting, writing, poetry, and so on. Arthur Rimbaud demands far more. He uses his works to characterize a space or time, a feeling or a representation that creates an opportunity to share something unique, and therefore his works often reach far deeper than expected. As you have pointed out in the question, his symbolism often explores a universal truth and once it is recognized, it cements and ingrains an often involuntary reaction in a way that language cannot do alone. In his letter of 1871 to Paul Demeny, Rimbaud makes his intention clear and states that he is only able to draw conclusions by personally experiencing all forms of "madness," ultimately arriving at the unknown. There is a danger that superfluous use of words or language that is only understood in a specific context become less defined because they are relevant only to specific sections of society. To Rimbaud, this weakens any real meaning and does not have the desired collective effect which almost serves to dismiss those artists.
The unconscious mind, in Freudian terms, operates as a defense mechanism wherein traumatic events and unimaginable wrongs may be stored in the mind in that place that allows people to continue on and function in the normal world. Inner conflict is avoided provided that those thoughts remain intangible and outside normal awareness. Actions are prompted by the conscious mind and reactions are often the result of the unconscious mind as it unknowingly affects those conscious actions. Even a cognitive psychological approach admits that abstract thinking, perception, and the ability to solve problems function within a realm which allows for interpretation and language use outside normal mental capacity.
For Rimbaud, involvement is central to the experience and the interpretation. He draws attention to horrific occurrences and suggests that without experience any art form becomes meaningless and therefore the artist himself and his works are fleeting. It is the "disordering of the senses" that creates the ultimate "seer" and it is the actual experience that ensures that truth is reached and can be interpreted so that a universal understanding results which is like a language itself. Rimbaud warns that interpretation becomes trivial when it exists only within a certain circle because it can only be interpreted on one level, thus losing its universality.
Therefore Arthur Rimbaud would support the premise that art is fleeting if it does not meet the criteria of deep and meaningful experiences which test the conscious and the unconscious mind. For art to make any real contribution to society, the artist must be able to reach inside himself so that his interpretation can be understood and serve a useful purpose, contributing to real life, ending unjust ideals and supporting far more than what he sees as mere artistic impression.