small and great, rich and poor, free and slave: Everyone must accept the beast's evil mark of ownership (see Revelation 14:9, 11; 19:20; 20:4). This mark is needed to buy or sell. The text does not clearly describe what the mark is or how it looks.
On the right hand or forehead suggests the branding of slaves, showing the beast owns them.
the name of the beast or the number of its name: In both Hebrew and Greek, letters of the alphabet stand for numbers, giving names a numerical value (Revelation 13:18).