I answer that, Since Happiness consists in gaining the last end, those things that are required for Happiness must be gathered from the way in which man is ordered to an end.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic happiness gain
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17897/pg17897-images.html

Context

“4:7, 8) : "I have fought a good fight, I have finished my course, I have kept the faith; as to the rest there is laid up for me a crown of justice." Therefore comprehension is necessary for Happiness.
I answer that, Since Happiness consists in gaining the last end, those things that are required for Happiness must be gathered from the way in which man is ordered to an end. Now man is ordered to an intelligible end partly through his intellect, and partly through his will: through his intellect, in so far as a certain imperfect knowledge of the end pre-exists in the intellect: through the will, first by love which is the will's first movement towards anything; secondly, by a real relation of the lover to the thing beloved, which relation may be threefold.” source