3 ideas
The title's idea, 'speech is capital', treats eloquence as an asset that can be invested, spent, and grown the way money is. A person with little wealth or power can use timely, well-chosen words to secure safety, favour, or advantage. A careless tongue loses that capital as surely as bad trading loses money.
Each story runs to a concrete outcome in which cleverness, patience, or honesty is rewarded, or greed, pride, or folly is punished. The narrator then states the lesson outright rather than leaving it implied. Pairing a vivid consequence with a named maxim makes the principle memorable and easy to repeat to others.
Stories drawn from Arabic, Persian, and European sources can become part of a local literature if their settings, customs, names, and idioms are fully recast into the audience's own world. The listener then receives them as Hausa stories rather than as translations. Deep cultural transposition, not literal rendering, is what let a foreign story stock found a new written prose tradition.