In the illustration many sheep are in an enclosure where several flocks come together for the night. The shepherd comes in the morning to lead them to their pasture, and he calls to his sheep by name. Though the individual flocks had become hopelessly intermixed during the night, the shepherd's sheep hear his voice and separate themselves from the larger flock.
Notice how often Christ emphasizes the voice of the shepherd in this short section: "The sheep hear his voice" (verse 3); "The sheep follow him, for they know his voice" (verse 4); "They do not know the voice of strangers" (verse 5). When the shepherd speaks, the sheep go to him immediately.
When "voice" is used in the New Testament, the writers all chose the Greek word phone, meaning "sound" or "spoken word." But phone can also mean "an address as to a group of people, a speech." Phone derives from phaino, meaning "to enlighten" or "to shine." From this root meaning springs the fact that phone can mean "disclosure" or "revelation" through an address or speech—a message!
This is its figurative meaning in John 10. The true and faithful shepherd will be preaching a message which his sheep will hear and immediately follow!
The Shepherd's Voice