In front of such a question, the correspondence between the art dualism and the knowledge dualism allows the reader to feel his own dualism based on the antagonism of the dionysian instinct with the Apollonian one. That is to say that the reader, by virtue of his natural human dualism, feels to embody with one of these two different conceptual characters, exactly Dionysus or Apollo, so that he is exposed to the dangerous unbalance of his own instincts.
On the one hand, indeed, the dionysian instinct is an unbalance in which the human being is the witness of a brutal and fleeting disclosure of truth. Therefore he lives the truth for a very short time through a debauched moment of inebriation in which he reconciles with Nature and with the god, but he loses himself. Human being is overwhelmed by the violent whole of truth.
On the other hand, the apollonian instinct is an unbalance in which human being lives the disclosure of truth through the artistic dream or the theoretical rationality. Therefore he lives the truth as a static and closed individualization that is, according to Nietzsche, the degeneration of the Attic tragedy whose representatives are Socrates and Euripides. The human being watches a single portion of truth from the safe distance of the symbol.
Thus the answer that the Greeks give to the Silenic truth is not the rational rigidity of apollonian condition, nor the unbridled dissolution of the Dionysian condition. It is indeed their balance which makes the dialogue they have in the drama of the Attic tragedy: “Thus drama is the Apollonian embodiment of Dionysiac insights and effects”.
The Dionysian inebriation and the apollonian form represent at the same time two opposite aesthetic expressions and two opposite form of knowledge of truth. Thus it is just the dialogue between these opposite ones that makes the best truth’s knowledge. It is quite a negative dialectics: the human being is dragged into the whole unbearable truth that overwhelms him; but he can set himself in the right distance to watch it from the outside. In this way human being can have a critical consciousness that allows him to make a clear analysis of truth.
In conclusion, Dyonisus and Apollo are the first conceptual characters of the “will to power” concept, because they embody the two different world view’s (weltanschauung) perspectives that Zarathustra goes beyond. Therefore the reader can identify with an existential condition in which he feels lost in his life, so much overwhelmed from what he lives that he cannot understand it (“lived” by his own existential condition); but he can identify too with another existential condition in which he feels lost in himself, so far from what he lives that he cannot relate to them (“detached” from his own existential condition).
In this way the reader can listen to the first note of the opening symphony of the Zarathustra’s sound, because this latter is the conceptual character of the “will to power” concept whose basis is the balance between Dionysus and Apollo. Therefore they are two “spirits”, as Nietzsche writes, two extreme parts of the same subject, the human being, and Zarathustra represents the human being who goes beyond his own dualism, who controls and uses their opposition as a tool to find an answer to the Silenic truth. For this reason Zarathsutra is the Übermensch.
Even if the reader can now listen to the first note of the Ouverture of the Zarathustra’s opera through The Birth of Tragedy, he cannot listen to the whole sound of Thus Spoke Zarathsutra’s enigma without another key note: the “gay science” concept. In Nietzsche’s philosophy, indeed, the conceptual character transition from Dionysus (and Apollo) to Zarathsutra cannot come true without the conceptual character of the Greek man that embodies the “gay science” concept. Therefore such a character has an originary self-consciousness in which he understands to be an individual and detached part of a Whole, so to get a feeling of insignificance and, at the same time, a liberating joy.
In this way the reader can re-emerge from the existential condition that overwhelms him, or he can re-conquer it if he feels completely detached, because the Greek man consciously accepts the human condition, so to be happy through it – and not in spite of it. It is what Nietzsche calls the “gay science”: a way through which man can handle the truth, living in a vital and positive pessimism that is the awareness of his human limit.
Therefore the conceptual character of the Greek man is the complete transition from the Dionysus/Apollo aesthetics to the ethics, because such a conscience is the weight and the privilege of the human being’s responsibility of his own strength and action. Nevertheless it is a responsibility resulted from what distinguishes the man from the animals, that is the weight and the privilege of memory and the consequent ability to dominate time.
A man who does not get such a conscience is dominated by the events that happen to him, because he does not live in a specific dimension of space and time. Anyway Nietzsche writes that the memory cannot exist without the oblivion, as the responsibility cannot exist without choice: man looks at the oblivious animals and understands that he could live like them, if only he would choose it. 
Thus the reader of The Gay Science can understand that he has the key choice of memory’s responsibility and freedom, giving up the passivity of the oblivion. He can find indeed a self-consciousness that is exactly the awareness of his temporal essence. He can understand that he is living in a history made of a specific space and time (hic et nunc) and that he can dominate it through the memory. That is the reason why such a conscience gives to the man the enthusiasm for his ability to act that Nietzsche calls “gay science”.