Moses and Aaron obeyed the Lord (see Exodus 7:6), and this is how God’s Word became reality. His Word does not return empty (Isaiah 55:11). He uses Moses and Aaron to execute his will and make it happen.
The staff changes into a serpent. It was likely a cobra, as a symbol of the power of the Pharaoh. The Pharaoh also had an image of a cobra on his forehead.
In Egypt, the cobra was honoured and feared, just as dictators (including the Pharaoh) were viewed with apprehension and, therefore, treated with respect; one must treat danger carefully.
Moses’s staff becomes the opponent of Pharaoh: God positions himself against the Pharaoh with the symbol of his might. The Pharaoh sees himself as the incarnation of the cobra goddess Wadjet, among others. Her power is in the image on his forehead. He scares the people with it (the Egyptians) and destroys his enemies (also Israelites). Everyone is afraid of him. But Moses stands as a god
before him (Exodus 7:1), and Moses places God’s power in opposition to the power of the Pharaoh. It is a frontal attack.
10 So Moses and Aaron went to Pharaoh and did just as the LORD commanded. Aaron cast down his staff before Pharaoh and his servants, and it became a serpent.