It is this light, itself lit from above, which gives the soul its brighter lifePlotinus
Enneads, Fifth Ennead (tr. Stephen MacKenna and B. S. Page)
Plotinus is describing something he can only point at. The light a soul carries is not its own — it is lit from above, and it burns brighter for it. He is not asking anyone to follow an argument. He is saying what happens when a person stops looking outward, and lets a light that was already there do its work.
From the Library: The Enneads, Plotinus