First we need to understand what Jesus used for his illustration. Shepherds back then used a community pin for nighttime and community wells to water the sheep. The way the shepherd separated his sheep from the rest was to call them, similar to how we would call a dog or cat today.
His legitimacy is further validated by the fact that the sheep listen to his voice. The relationship between the shepherd and his sheep is so deep and longstanding that he can call them by name. The depiction here is of a shepherd beginning the workday by gaining entrance through the night watchman and calling each of his beloved sheep by names he has given to them (Fuzzy? Wooly? Sparky?). They respond to his summons, and he leads them out to their daily grazing area. The story pictures a community sheep pen where several flocks are housed together. During the night the sheep from various flocks may have intermingled. This shepherd does not separate his sheep by walking through the pen, but by standing at the gate and calling their names. --
Bryant, B. H., & Krause, M. S. (1998). John (John 10:2–3). Joplin, MO: College Press Pub. Co.
What Jesus said about his voice outside the figure of speech (τὴν παροιμίαν):
- Jesus laid down his life for those who believe in him (v.11).
- Jesus equates the words he spoke during his earthly ministry with “his voice” in the figure of speech (vs.25-28).
- John 16:8-14 points to the ministry of the Holy Spirit as being “his voice.”
8 And when he [the Holy Spirit] comes, he will convict the world concerning sin and righteousness and judgment: 9 concerning sin, because they do not believe in me; 10 concerning righteousness, because I go to the Father, and you will see me no longer; 11 concerning judgment, because the ruler of this world is judged.
12 “I still have many things to say to you, but you cannot bear them now. 13 When the Spirit of truth comes, he will guide you into all the truth, for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come. 14 He will glorify me, for he will take what is mine and declare it to you.
(John 16:8–14, ESV)
Thus, Jesus’ voice is his words as recorded in the Bible and the prompting of the Holy Spirit in our lives to believe his word.
Note: We can make this too simple if we only take this as mental belief. That is hearing Jesus' voice but not necessarily responding to it. Responding to Jesus' voice means doing what he said.
15 “If you love me, you will keep my commandments. 16 And I will ask the Father, and he will give you another Helper, to be with you forever, 17 even the Spirit of truth, whom the world cannot receive, because it neither sees him nor knows him. You know him, for he dwells with you and will be in you. (John 14:15–17, ESV)
Comforting however is Jesus searches for his lost sheep. None of us are perfect.