The kingdom of heaven is said to be bought when a man gives what he has for God's sake.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic heaven God
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

“Nor does everyone sin against the Holy Ghost that sins from choice, but only he who chooses sin through contempt of those things whereby man is wont to be withdrawn from sin, as stated above (Q. 14, A. 1) . Reply Obj. 3: The kingdom of heaven is said to be bought when a man gives what he has for God's sake. But this is to employ the term "buying" in a wide sense, and as synonymous with merit: nor does it reach to the perfect signification of buying, both because neither "the sufferings of this time," nor any gift or deed of ours, "are worthy to be compared with the glory to come, that shall be revealed in us"” source