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Of course, he who has put forth his total strength in fit actions has the richest return of wisdom. I will not shut myself out of this globe of action, and transplant an oak into a flower-pot, there to hunger and pine; nor trust the revenue of some single faculty, and exhaust one vein of thought, much like those Savoyards, who, getting their livelihood by carving shepherds, shepherdesses, and smoking Dutchmen, for all Europe, went out one day to the mountain to find stock, and discovered that they had whittled up the last of their pine-trees. Authors we have, in numbers, who have written out their vein, and who, moved by a commendable prudence, sail for Greece or , follow the trapper into the prairie, or ramble round , to replenish their merchantable stock.

If it were only for a vocabulary, the scholar would be covetous of action. Life is our dictionary. Years are well spent in country labors; in town; in the insight into trades and manufactures; in frank intercourse with many men and women; in science; in art; to the one end of mastering in all their facts a language by which to illustrate and embody our perceptions. I learn immediately from any speaker how much he has already lived, through the poverty or the splendor of his speech. Life lies behind us as the quarry from whence we get tiles and copestones for the masonry of to-day. This is the way to learn grammar. Colleges and books only copy the language which the field and the work-yard made.

http://www.oldandsold.com/articles33n/essays-studies-6.shtml

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The underlined part is difficult.
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I believe it means:

"The scholar would be covetous of [i.e. would desire] 'action' [which here seems to mean something like 'seeing the world', or 'seeing many different aspects of life'] even if the only benefit of that 'action' was to provide him with a richer vocabulary with which to express himself."
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Thanks a lot, Mr Wordy !!