Thus the worth of any object to be acquired by our action is always conditional. Beings the existence of which rests not on our will but on nature, if they are beings without reason, still have only a relative worth, as means, and are therefore called things, whereas rational beings are called persons because their nature already marks them out as an end in itself, that is, as something that may not be used merely as a means, and hence so far limits all choice (and is an
I think he is saying that we as humans are not be to used as means to end. To do so would be ethically wrong.