After this third stanza and final, repetitive line of "They Lion grow," I believe "they" is used as referring to society, the government, or authorities. "Lion" sounds as if it is referring to a specific group of people or class, maybe even a race. Each stanza before seems to give characteristics or actions of what "Lion" people do that distinguishes them from those who are not "Lion." If the line was rephrased from "they Lion grow" to "they grow Lion," the meaning could be similar.
Also, the noun "Lion" makes me curious as to why that title was chosen to label a certain group of people (if that was the intention) because lions themselves can be defined by people very differently. To some, lions are majestic, strong, and inferior, whereas to others, lions are described as frightening, aggressive, threatening, etc.