"As we meditate upon these thoughts we are able to go a step further and see that man acts on three planes: THOUGHTS (in the unconscious realm), then WORDS (in the conscious realm), and finally, a culmination of both manifested as DEEDS performed by the physical body. If we have understanding to count it, as John said, we are able to see here the number of the beast. MAN’S number is SIX - and SIX in the realm of thought, then SIX raised to a higher power in the realm of words, and finally SIX raised to yet a higher power in the realm of deeds is 666 which = flesh, FLESH, F-L-E-S-H! Ah, who is the beast? And what is his number? It is MAN - MAN exalting HIMSELF as God, usurping God’s glory, taking the precious things of the Spirit and misusing them for his own purposes and aggrandizement."
"While we once looked anxiously about for a social security number, a credit card number, or a laser-tattooed identification number to be the “mark of the beast” was it not truly there for us to see all along, for John plainly told us: “HERE IS WISDOM. Let him that has understanding count the number of the beast; for it is the NUMBER OF MAN and HIS NUMBER is SIX HUNDRED, THREESCORE AND SIX.” The indefinite article “a” which appears in the King James translation is supplied by the translators and is not necessarily included in the Greek, since that language has no indefinite article. In symbolism, furthermore, NUMBER is used to denote the characteristics or the nature of a thing. Thus, the NUMBER OF THE BEAST is the NATURE of the beast, and the number 666 is shown to be the NATURE OF MAN Even if we include the indefinite article so that reads, “For it is the number of a man,” this does not in any case mean that the beast is “a man” for the “number of a man” means the measure of a man, that is, his inward state of being manifested by his outward actions, and how these are perceived by those about him."
Much more in the link:
https://www.kingdombiblestudies.org/antichrist/antichrist1.htm#10
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"On that distant day upon the plain of Dura Nebuchadnezzar’s image of gold was sixty cubits high and six cubits wide. We notice that the Church system is never satisfied with GOD ALONE, but is always building images - images of organization, system, ceremony, ritual, program, etc., as Nebuchadnezzar did, so that all their subjects should worship that image. In Revelation thirteen a mysterious number is attached to the beast and his image, called the “number of his name”, and special attention is called to it by the Holy Spirit. In the book of Revelation especially, the number seven is, as elsewhere throughout the Scriptures, prominent as the sacred number of completeness and perfection. The contents of the book opened by the Lamb is contained under seven seals, seven trumpets, and seven vials - a TRINITY OF SEVENS. It is in this book that the “number” of the beast is also represented as a TRINITY OF SIXES, and the contrast, as well as the intrinsic meaning of the number, intimates, that whatever else it may be, it is a perfect number of imperfection, or rather a number denoting PERFECT IMPERFECTION. In the Bible the number six refers to man - it is a human number. Man was created on the sixth day, man’s appointed days of labor and toil are six, the Hebrew slave was to serve for six years, and for six years the land was to be sown. Six is the number of man’s unredeemed nature, Old Adam - THE FLESH."