Revelation 13:11 And I beheld another beast coming up out of the earth; and he had two horns like a lamb, and he spake as a dragon. 12 And he exerciseth all the power of the first beast before him, and causeth the earth and them which dwell therein to worship the first beast, whose deadly wound was healed. 13 And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men, 14 And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live. 15 And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed. 16 And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads: 17 And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name. 18 Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six.
A beast represents a political power. The first beast represents the Roman Empire. Constantine moved the centre of government from Rome to Constantinople. This left somewhat of a power vacuum in Rome.
The Roman Church eventually received temporal power by an alliance with the Franks and thus became the beast with two horns like a lamb.
From this alliance came what is known as the ‘Holy Roman Empire’. This was ‘the image of the first beast’.
The Papacy exercised power over kings. The Church had power over individuals from cradle to grave, its rules being enforced by the secular powers. This continued until the ‘Reformation’ following which the Papal temporal power was lost.
Buying and selling is a metaphor for preaching and hearing the gospel; as seen in Isaiah 55.
Isaiah 55:1 Ho, every one that thirsteth, come ye to the waters, and he that hath no money; come ye, buy, and eat; yea, come, buy wine and milk without money and without price.
Whilst the Church was in power no one was allowed to preach (i.e. sell) or listen to (i.e. buy) the preaching of the gospel without the permission of the Church.
The history of the Lollards and others testifies to the truth of the suppression exercised by the Roman Church.
The mark in the right hand and on the forehead refers to the practice of ‘priests’ signing the cross upon those favoured by the Church; usually with ‘holy water’.
The number 666 can be derived by adding the numerical value of the letters making up the Greek name ‘Lateinos’, which, in plain English, may be said to mean Latindom or Latin power, kingdom, or Church headed up in the Papacy.
I hope you find this helpful.