He wondered ... - What particularly attracted his attention was the fact that the bush was not consumed, Exodus 3:2-3.
The voice of the Lord - Yahweh spake to him from the midst of the bush. He did not see him. He merely heard a voice.
Related Commentaries of Acts 7:31
Acts 7:31
31 When Moses saw it, he wondered at the sight: and as he drew near to behold it, the voice of the Lord came unto him,