Albert Barnes Commentary Acts 7:31

"And when Moses saw it, he wondered at the sight: and as he drew near to behold, there came a voice of the Lord," — Acts 7:31 (ASV)

He wondered, etc. What particularly attracted his attention was the fact that the bush was not consumed (Exodus 3:2–3).

The voice of the Lord. Jehovah spoke to him from the midst of the bush. He did not see him, but he simply heard a voice.