‘Blessed be Yahweh, the God of Shem, and let Canaan be his servant.'
This is an unusual phrase as we expect to read ‘blessed be Shem'. It arises from the fact that Noah sees the greatness of the blessing that is to be Shem's and is consequently filled with wonder and praise to Yahweh. The purpose is to draw out that Shem is to be blessed because of his relationship to Yahweh rather than just because of his own status. Shem's descendants will be especially blessed, they will include the race through which God's revelation will come to men. But this will be of God's unmerited favour and goodness, and beyond anything that Shem deserves. (Compare Genesis 24:27 where a blessing on Yahweh includes a blessing on the servant of Yahweh).