In order to "tell the Church" (singular noun), it must be both known and visible. There cannot be a multiplicity of different churches. Nor can it be a strictly mystical entity. Note also that it must have existed from apostolic times, and have a continuous existence since that time, otherwise this scriptural directive could not be carried out. No Protestant organization can fulfill this role.
For the Church to speak with one voice, it must be both visible and knowable. And the doctrine that is taught must be a single, coherent whole as well. Otherwise a single coherent answer could not be delivered and heard.