It's not so much a matter of only believing that Jesus was the Son of God, but a call to listen to him, to hear him speak to us. Jesus is calling all people into a close, intimate relationship with him and through him to God. This is an unparalleled intimacy of the Father and the Son, of divinity interacting with humanity. And the power of that intimacy is made real not through intellectual acrobatics and reasoned thought, but when we hear his voice. The relationship between the shepherd and his sheep is a close one.
Sheep are dumb, passive animals.
Comparing humans to sheep is not always a favorable metaphor. But the point is that the sheep are dependent upon the shepherd for their well-being, for their safety. The shepherd cares for the sheep. When I lived in Scotland, I learned that when shepherds want to move sheep from one field to another, the shepherds, with the help of sheep dogs, drive the sheep from behind. This is in contrast with shepherds in the middle east, where even to this day, the shepherd leads the way at the head of the flock and the sheep follow.