What does Genesis 48:19 mean?

But his father refused. He said, 'I know, my son, I know. Manasseh will become a people, and he’ll be important. But his younger brother will be even greater, and his descendants will become a whole group of nations.' Genesis 48:19 - Modern Text Bible

(Jacob knowingly blesses the younger son, Ephraim, predicting that his descendants will surpass Manasseh’s.)