Why is good will considered good without qualification and how is it different from other good things?

For Kant, the very essence of an action to be considered morally good is the principle that a person affirms when he/she wills an action. As the philosopher himself explains: "The good will is good not because of what it causes or accomplishes, not because of its usefulness in the attainment of some set purpose, but alone because of the willing, that is to say, it is good of itself." Thus, for Kant, the good will does exclude the other goods (moderation of the passions, happiness, etc), but according to him, the other goods cannot be called "without qualification" because they are not ends in themselves; i.e., they are sought for the sake of something else. That, for Kant, cannot be called "without qualification."