We use it when emphasizing that we refer to one particular thing. For instance, "It is Lawrence you should be talking to". Or, "It was malaria that killed him." What pronoun should we apply when we want to emphasize plural things? it does not look all right in such scenario. Should we use "they"? For instance, "It is we that will win this match." Here I doubt I can still use "it", but I do not find another pronoun. If "it" can be used here, that means sometimes "it" refers to plural things.