In the beginning, the very first action of God is recorded as Him speaking. The entirety of the creation story in Genesis 1 is laced with the voice of God. If you are to take the Genesis story at face value, you would have to come away with a belief that the Being who created all is one who speaks. And then, on the sixth day, God creates man and woman in His image. How does He do this? By speaking:
Genesis 1:26a Then God said, “Let Us make man in Our image…”
The very first interaction He has with these creatures is through Him speaking:
Genesis 1:28 Then God blessed them, and God said to them, “Be fruitful and multiply; fill the earth and subdue it; have dominion over the fish of the sea, over the birds of the air, and over every living thing that moves on the earth.”
The most normal thing for Adam and Eve to expect when engaging the One who created them was that He would speak.