[T]he artist sells the work of his brush and in this he is a merchant. The writer sells to any who will buy, let his ideas be what they will. The teacher sells his knowledge of books—often in too low a market—to those who would have this knowledge passed on to the young.
The doctor... too is a merchant. His stock-in-trade is his intimate knowledge of the physical man and his skill to prevent or remove disabilities. ...The lawyer sometimes knows the laws of the land and sometimes does not, but he sells his legal language, often accompanied by common sense, to the multitude who have not yet learned that a contentious nature may squander quite as successfully as the spendthrift. The statesman sells his knowledge of men and affairs, and the spoken or written exposition of his principles of Government; and he receives in return the satisfaction of doing what he can for his nation, and occasionally wins as well a niche in its temple of fame.
The man possessing many lands, he especially would be a merchant... and sell, but his is a merchandise which too often nowadays waits in vain for the buyer. The preacher, the lecturer, the actor, the estate agent, the farmer, the employé, all, all are merchants, all have something to dispose of at a profit to themselves, and the dignity of the business is decided by the manner in which they conduct the sale.

What It Means

This is a placeholder explanation generated by the low-overhead model. It interprets "[T]he artist sells the work of his brush and in this he is a merchant. The writer sells to any who will buy, let his ideas be what they will. The teacher sells his knowledge of books—often in too low a market—to those who would have this knowledge passed on to the young.
The doctor... too is a merchant. His stock-in-trade is his intimate knowledge of the physical man and his skill to prevent or remove disabilities. ...The lawyer sometimes knows the laws of the land and sometimes does not, but he sells his legal language, often accompanied by common sense, to the multitude who have not yet learned that a contentious nature may squander quite as successfully as the spendthrift. The statesman sells his knowledge of men and affairs, and the spoken or written exposition of his principles of Government; and he receives in return the satisfaction of doing what he can for his nation, and occasionally wins as well a niche in its temple of fame.
The man possessing many lands, he especially would be a merchant... and sell, but his is a merchandise which too often nowadays waits in vain for the buyer. The preacher, the lecturer, the actor, the estate agent, the farmer, the employé, all, all are merchants, all have something to dispose of at a profit to themselves, and the dignity of the business is decided by the manner in which they conduct the sale." in the context of "" to mean that wisdom is timeless.