it is a responsibility though??
This simile is intended to create a tone of humor.
All of the Athenian's interjections become puns played off of the dialogue in "Pyramus and Thisbe" or off of each other's lighthearted criticisms of the play. Lysander here is comparing Quince's reading of the prologue to a person who does not know how to ride a difficult horse (jolty, not knowing where or how to stop). This sets up the tone for more jokes as the play within the play continues.
The sentence structure contributes to the passage because it helps to find textual evidence
