Jesus is speaking of His pending crucifixion, referring to it as 'His hour" (vs 27). He explains that He has come for that express purpose and that it was His desire to do so and 'glorify the Father."
Suddenly, God speaks, answering His Son (vs 28). This should come as no surprise, for in John 11:42, Jesus said to the Father, "I know that thou hearest me always..." But, the thing that caught my attention is how the people responded to what they heard (vs 29).
Hearing the same sounds, some thought it thundered, while others thought they heard an angel speak. Both groups agreed that they heard something, but could not distinguish (understand) just what they had heard.
Maybe they were not expecting God to speak, or, maybe they did not recognize God when He spoke. Some heard distinctly "an angel spoke" while others heard indistinctly "it thundered", ie, the heard a noise, but could not distinguish it as a 'voice'.
We read that God spoke 'for their sakes', but some did not hear...which begs the question:
What do you hear when God speaks? It is not a question of whether God speaks, for He has. See Psalm 19 and Hebrews 1:1-2. The question is, 'do you hear God when He speaks? do you hear distinctly, or is His voice muffled?"
Do you expect to hear Him speak when you read His Word...supposing that you do read it. Do you recognize His voice in a song or a sermon? Are you expecting Him to speak to you? Do you have 'ears to hear what the Spirit says"?
If not, why not?
Fanny Crosby wrote, "Jesus Is Calling"...give a listen!