"The thing of greatest importance here is the awful fact that, before ever man’s HAND was extended and the transgression committed, that old serpent, the king of the bestial system, the devil, had IMPARTED HIS MIND TO THEM. The MARK OF THE BEAST was in their hearts, in their MINDS, and in their FOREHEADS, and what they did afterward was the MARK OF THE BEAST in their HANDS. It is not difficult to see that the things which men are doing today and have done in ages past are but the MANIFESTATION of that which is in their minds, for, “As a man THINKS in his heart, so is he” (Prov. 23:7) and “a good man out of the good treasure of the heart brings forth good things; and an evil man out of the evil treasure brings forth evil things” (Mat. 12:34-35). The mark of the beast that appears IN THE HAND (outward actions) is the direct result of the mark of the beast IN THE FOREHEAD (mind, nature). This is the mind that inspires the ever increasing confusion and violence that is running rampant among all nations."
In depth study on the mark in the link:
https://www.kingdombiblestudies.org/antichrist/antichrist1.htm#6
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"A comparison of Gen. 17:11 with Rom. 4:11, and Rev. 7:3 with Eze. 9:4 (and numerous other passages) shows that the words “token”, “sign”, “seal”, and “mark” are used in the Bible as synonymous terms. Thus, the “SEAL of God in the forehead”, the “Father’s NAME in the forehead”, and the “MARK of the beast in the forehead” all indicate the same principle at work. In this case it is not some literal mark to be made in the flesh, but a state of being in mind and nature which serves as a “mark of distinction” between those who are HIS and those who are of the beastly system of the world."
https://www.kingdombiblestudies.org/antichrist/antichrist1.htm#7
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