>>115869353His thematic substance is to counter Venom's theme of dependancy by offering a check to Venom's more violent tendencies & a way to direct them in a more lawful (i.e goverment handled) manner. He wants Brock to stop using the symbiote to fill the whole in his life & he wants the symbiote to be in a more supportive, nurturing environment
i.e, Flash's body. Anti-Venom is just his way of forcing that choice onto both of them.
For a anti-hero like Venom, Flash is basically Captain America