John Gill's Exposition of the Whole Bible
Proverbs 21:20
[There is] a treasure to be desired,.... Gold, silver, jewels, and precious stones; all sorts food, as Aben Ezra explains it, and rich and costly, raiment; all which may be lawfully desired and sought after, and, when obtained, laid up for future use; which may be spared for their own service and that of posterity: but there are riches of grace, a pearl of great price and treasure in heaven, more desirable than these, Matthew 6:19;
and oil in the dwelling of the wise; which is particularly mentioned, because a principal blessing of the land of Canaan; much used for food, and was for delight and refreshment: and something of this was in the house of every wise, provident, and industrious man, for the use of him and his family; even though he lived but in a "cottage", as the word f signifies this is an emblem of the grace of God, which is sometimes compared to oil; which a wise man is chiefly concerned, that it may be in his heart, in his house, and in his family;
but a foolish man spendeth it up; the oil; he swallows it up at once, as soon as he has got it, and wastes and lavishes away what his wise father had provided for him. This may refer not to oil only, but to the desired treasure, wealth, riches, substance of every sort, he is heir to and becomes possessed of; and which, in a spiritual sense, may be applied to a foolish wicked man, who misspends his time, neglects the means of grace, and all opportunities by which men grow rich and wise in spiritual things; see Matthew 25:1.
f נוה "tuguirolum", Mercerus, Gejerus.