en_tn_condensed/rev/13/17.md

It was impossible for anyone to buy or sell unless he had the mark of the beast

"People could buy or sell things only if they had the mark of the beast." The implicit information that the beast from the earth commanded it can be stated clearly. Alternate translation: "He commanded that people could buy or sell things only if they had the mark of the beast" (See: rc://en/ta/man/translate/figs-explicit)

the mark of the beast

This was an identifying mark that indicated that the person who received it worshiped the beast.