We are familiar with the concept of a spokesman or spokesperson. It’s a person who speaks for another person or group.
Zizi Kodwa is the South African presidential spokesmen. What Zizi says, the SA president says.
Sean Spicer, probably has one of the worst jobs in the world, he is the current spokesperson for President Donald Trump. Officially he is the White House Press Secretary. What Sean Spicer says Donald Trump says. Mr. Spicer must also explain what Donald Trump says and tweets.
Individuals and organizations have official spokesmen who speak for them or the organization.
One of the functions of the Holy Spirit, the third person of the Triune God, is to be the spokesman of God.