The night and the potion are two symbols used by Shakespeare to establish two themes in the story. Furthermore, the families of Romeo and Juliet are the people who represent something "bigger" in the story.
We can arrive at this answer because:
The night is one of the great symbols used by Shakespeare to represent the mystery and unpredictability of love.
This can be seen, as it is during the night that the most significant and most unpredictable moments between Romeo and Juliet happen.
It's during the night that they meet, communicate, decide to get married and die.
Another important symbol in the story is the potions, which represents the deadly rivalry between families.
It is through a potion that Juliet simulates her own death so that the family does not interfere in her marriage. This results in the ingestion of the poisonous potion that Romeo ingested that caused his death.
These two potions would not be ingested if the rivalry between the families did not exist.
Both Romeo and Juliet's families are people who represent something very big in the plot. This is because all the events in the story revolve around the rivalry between the two families, which is maintained between generations.
