The theme that Mr. Hooper's dialogue in lines 18-19 best foreshadows is this: People fear what they do not understand.
What is the foreshadowing?
Trying new things can be scary, especially if they are outside of our comfort zone. We may worry about failing, being judged, or simply not knowing what to expect. These are seen in the dialogues in lines 18 and 19.
In addition, change can be disruptive and unsettling, even if it is ultimately positive. We may fear the loss of control or the unknown consequences of change.