The original "be fruitful and multiply" blessing given to the first humans — repeated here verbatim after the flood.
God blessed Noah and his sons, and said to them, “Be fruitful, multiply, and replenish the earth.
God blessed them. God said to them, “Be fruitful, multiply, fill the earth, and subdue it. Have dominion over the fish of the sea, over the birds of the sky, and over every living thing that moves on the earth.”
Noah receiving the same "be fruitful and multiply" blessing given in Eden casts him, briefly, as a candidate for the promised "seed of the woman" who would undo the serpent's damage (Genesis 3:15). It doesn't last — a few verses later Noah gets drunk, ends up exposed, and the whole family drama repeats a version of Eden's shame. Genesis is being honest about its own hopes here: Noah advances the story toward its eventual deliverer without being that deliverer himself.