Hence it can be argued that, if any man loves not his neighbor, neither does he love God, not because his neighbor is more lovable, but because he is the first thing to demand our love: and God is more lovable by reason of His greater goodness.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic goodness love
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/18755/pg18755-images.html

Context

“For, since our neighbor is more visible to us, he is the first lovable object we meet with, because "the soul learns, from those things it knows, to love what it knows not," as Gregory says in a homily (In Evang. xi) . Hence it can be argued that, if any man loves not his neighbor, neither does he love God, not because his neighbor is more lovable, but because he is the first thing to demand our love: and God is more lovable by reason of His greater goodness. Reply Obj. 2: The likeness we have to God precedes and causes the likeness we have to our neighbor: because from the very fact that we share along with our neighbor in something received from God, we become like to our neighbor.” source