Full Idea
Kant's fundamental sermon is that a value is made a value (or, at least, a duty) by human choice and not by some intrinsic quality in itself, out there. Values are what humans freely choose to live, fight and die for.
Gist of Idea
Values are created by human choices, and are not some intrinsic quality, out there
Source
report of Immanuel Kant (Groundwork of the Metaphysic of Morals [1785]) by Isaiah Berlin - The Roots of Romanticism Ch.4
Book Reference
Berlin,Isaiah: 'The Roots of Romanticism' [Pimlico 2000], p.72
A Reaction
If this is right, then it would appear that the great Kant is the father of relativism, which wouldn't please him. However, his whole system rests on what is consistent and rational, and that seems to a value that is above our choices.