For whatever belongs to nature is the material part of an order; whilst that which perfects is from grace which depends on the liberality of God, and not on the order of nature.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic God grace
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17611/pg17611-images.html

Context

“In view of this distinction, some asserted that men can in no way be transferred to an equality with the angels; but this is erroneous, contradicting as it does the promise of Christ saying that the children of the resurrection will be equal to the angels in heaven (Luke 20:36). For whatever belongs to nature is the material part of an order; whilst that which perfects is from grace which depends on the liberality of God, and not on the order of nature. Therefore by the gift of grace men can merit glory in such a degree as to be equal to the angels, in each of the angelic grades; and this implies that men are taken up into the orders of the angels. Some, however, say that not all who are saved are assumed into the angelic orders, but only virgins or the perfect; and that the other will constitute their own order, as it were, corresponding to the whole society of the angels.” source