Topics are opinions. Opinions are only ideas that have been turned over in the mind to the point we accept them as some type of truth. But basically we have opinions based on three things: (physical) body (psychological (mind) and Spirit. The first of these contains so much, e.g. our health, food, rest, exercise, we have opinions on these things.
The second of these engenders most of the 'topic matter' - opinions on all manner of subjects. Ideas held in the mind vs ideas held in others' minds. These can become so believable that people will go to war agains people who have different opinions. As some Zen Master once said: "Forget about truth, just don't cherish opinions."
And the third - and most important - deals with something we might look to others for opinions but, in the end, have to delve into ourselves - our spirit and the perenial question, "What am I?" The search and the journey has to be made by us individually.
There is a quote in the book, 'A Course of Miracles': Nothing real is threatened, nothing unreal exists; therein lies the peace of God. In the long run, nothing matters. It is our ego-minds, our self-image concepts which make topics matter.