Or HaChaim on Exodus 4:2/אור החיים על שמות ד׳:ב׳

1 ?זיאמר ה׳ מזה בידך "G'd said: "what is this in your hand?" This question cannot be compared to when G'd asked Bileam (Numbers 22,9) "who are these men?" Our sages in Bamidbar Rabbah 19 state that Bileam should have answered G'd that He was well aware of even a chamber-pot Bileam had in his bedroom, how much more so would He be aware of who the messengers were who had come to him that evening? However, the two situations cannot be compared. When G'd asked Bileam who the men were who had come to him, Bileam had some excuse to assume that G'd really was not aware of their identity; When He asked Moses what the latter held in his hand, it was daylight and G'd had obviously seen it. The question therefore could only be a rhetorical one. G'd only wanted Moses to confirm what it was he held in his hand. Moses complied and said "it is a staff."