Psychologically, will pass is the subject. Uhland meant, What will pass before your eyes is a tragedy. Accord between syntactical and psychological organization is not as prevalent as we tend to assume - rather, it is a requirement that is seldom met. Not only subject and predicate, but grammatical gender, number, case, tense, degree, etc. have their psychological doubles. A spontaneous utterance wrong from the point of view of grammar, may have charm and aesthetic value.
Absolute correctness is achieved only beyond natural language, in mathematics.
Our daily speech continually fluctuates between the ideals of mathematical and of imaginative harmony. A simplified syntax, condensation, and a greatly reduced number of words characterise the tendency to predication which appears in external speech when the partners know what is going on. In complete contrast to this kind of understanding are the comical mix-ups resulting from people's thoughts going in different directions. He led away my cow. That meadow was my father's land in days gone by.