In this statement, opportunity is referred to as a door. The author thus directly refers to opportunity by comparing it to a door. The figure of speech that this statement represents is Metaphor.
Metaphor is a figure of speech that refers to something by describing it as another thing. In this statement, the author mentions the door of opportunity.
While opportunity is not literally understood to be a door, symbolically, it makes way for so many things.
Therefore, the author applies metaphor in this instance.
