What does Genesis 9:7 mean?

This verse wraps up the section of blessings and commands by repeating the contents of verse 1: Noah, his sons, and all humanity to follow were charged with having more and more children and filling up the earth again. Implied in the command is God's blessing to make it possible for humanity to continue to reproduce, to continue to receive the gift of children from God's hand through the process of human reproduction.

God had wiped out humanity for its sinfulness, but God's intent is for humanity to thrive again under a new and reestablished relationship with Him.

The repeat of this command is also important in that it follows God's specific call for severe punishment in cases of murder. In verse 6, God institutes a requirement that any man or animal who murders a human being is to be put to death. The reason given was due to man's status as an image-bearer of God. Here, by returning to the issue of expanding the human race, we see a second reason for God's harsh stance against murder. Rather than allow the kind of violence which had ruined the pre-flood world, God sets a new standard.