He says it all right here...
Man is created to praise, reverence, and serve God our Lord, and by this
means to save his soul.
And the other things on the face of the earth are
created for man and that they may help him in prosecuting the end for which he
From this it follows that man is to use them as much as they help
him on to his end, and ought to rid himself of them so far as they hinder him as
For this it is necessary to make ourselves indifferent to all created
things in all that is allowed to the choice of our free will and is not
prohibited to it; so that, on our part, we want not health rather than sickness,
riches rather than poverty, honor rather than dishonor, long rather than short
life, and so in all the rest; desiring and choosing only what is most conducive
for us to the end for which we are created.