To whom he said - To whom God had said; that is, to the Jews. He had taught them the way of rest through the prophets, but they had refused to learn.
This is the rest - That is, this is the true way of happiness, to wit, by keeping the commands of God which had been so often repeated as to become to them objects of satiety and disgust.
This is the refreshing - This is the way in which the mind may be comforted.