606. 13:17 So that no one can buy or sell if he does not have the mark or the name of the beast, or the number of its name. This symbolically means that no one is allowed to teach from the Word, or consequently to be inaugurated into the priesthood, to be accorded the badge of the teaching office, to be granted the doctor's cap, and called orthodox, but one who acknowledges that doctrine and swears to a belief in it and love for it, and to such as is in conformity with it, or such as does not conflict with it.
To buy and to sell mean, symbolically, to acquire concepts, in this case concepts having to do with that doctrine, and to teach them, as shown below. The mark of the beast symbolizes an acknowledgment that one is a Reformed Christian, and a confession that one is such (no. 605). The name of the beast symbolizes the character of the doctrine, a name symbolizing character (nos. 81, 122, 165, 584), and the beast symbolizing the doctrine accepted by the laity, thus by the general populace (no. 567). Moreover, because the verse says "or the name of the beast," it symbolizes its character or such as is in conformity with it. A number symbolizes the character of a thing (no. 448), and because the verse says "or the number of its name," it symbolizes the character of the doctrine or such as does not conflict with it.
It is stated so, because the doctrine symbolized by the dragon and its beast is not the same throughout the kingdoms in which Reformed Protestants are found, though it is the same in respect to this postulate or principal tenet of the doctrine, that faith justifies and saves apart from works of the law.
 That to buy and to sell mean, symbolically, to acquire concepts for oneself and to teach them, and so likewise to market, trade, and make a profit, is clear from the following passages:
Everyone who thirsts, come to the waters; and you who have no money, come, buy and eat. Yes, come, buy wine and milk without money... (Isaiah 55:1)
You have sold yourselves for nothing; (therefore) you shall not be redeemed with money. (Isaiah 52:3)
With your wisdom and your understanding you have gained riches for yourself...; by your great wisdom in your trading you have increased your riches... (Ezekiel 28:4-5)
Since Tyre symbolized the church in respect to its concepts of goodness and truth, therefore we are told the following concerning Tyre:
All the ships of the sea... were... to market your merchandise... Tarshish was your trader...(in) silver... Javan, Tubal, and Meshech were your merchants. With human life... they carried on your trading... Syria was your trader... with chrysoprase... Your riches, your wares, and your merchandise..., ...those carrying on your trade..., will fall into the midst of the seas on the day of your ruin. (Ezekiel 27:9, 12-13, 16, 27)
Wail, you ships of Tarshish! For (Tyre) is laid waste..., whose merchants are princes, and whose traders are the honored of the earth? (Isaiah 23:1-8)
Trading has the same meaning in the Lord's parable about a man traveling to a far country, who gave his servants talents to trade with and make a profit (Matthew 25:14-30). In another parable about a man who gave his servants ten minas for them to do business with (Luke 19:12-26). In the parable regarding a treasure hidden in a field, which a man found and hid, who sold all that he had and bought the field (Matthew 13:44). And in the one about a man seeking beautiful pearls, who, when he had found one precious one, sold all that he had and bought it (Matthew 13:45-46).
Such have they become..., your merchants from your youth; they shall wander each one from his region, not saving you. (Isaiah 47:15)
And so on elsewhere.