John Calvin Commentary Acts 9:7

"And the men that journeyed with him stood speechless, hearing the voice, but beholding no man." — Acts 9:7 (ASV)

And the men. He now speaks briefly about Paul's companions, stating that they were witnesses of the vision. Yet it seems that this narration does not in all points agree with Paul's account, which we will see in the 22nd chapter (Acts 22:9). For he will say there that his companions were terrified by the light, but they heard no voice.

Some think that it was a mistake, and that through the writer's ignorance, the negation is misplaced. I think this is not difficult to answer, because they may have heard the sound of the voice, yet they did not discern either who spoke or what was spoken.

He says, “They heard not,” and then, “the voice of him that spake with me.” Surely, this is the meaning of these words: that Paul alone understood Christ's words. It does not follow from this, however, that the others might not have heard a muffled and indistinct voice.

While Luke says in this passage that a voice was heard and no one was seen, he means that the voice did not come from any human, but was uttered by God. Therefore, so that the miracle might be more credible, Paul’s companions see a light like lightning; they see Paul lying prostrate; they hear a voice (though not distinctly) sounding from heaven; and yet, nevertheless, Paul alone is taught what he must do.