The sheep, like the lover in Song of Songs 2:14, know the voice because they know the Shepherd and trust Him. They trust His voice. In it, they hear safety, security, sustenance, joy, hope, encouragement, love, warmth, and correction that does not turn them aside. The voice is the effective means of communication between Christ and us. The voice not only identifies, but it also communicates concepts to us that reveal both character and emotion.
John W. Ritenbaugh
Unity (Part 4)