I have a theory with enough Biblical support to decode the number of this man who is 666 from Rev 13:18. I have reason to believe that this man is fallen Adam, who was deceived by Satan to receive his own righteous standard which was passed down to all his progeny through procreation. This nature of rebellion against God that comes from men who are each a law to themselves from fallen Adam is the spirit of Anti-Christ (1Jn 4:3 & 2Jn 1:7).

Deut 6 (Christ Law)
8 And thou shalt bind them for a sign upon thine hand, and they shall be as frontlets between thine eyes.

Rev 13 (Anti-Christ Law)
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.

Have you ever wondered, what it is to be a law to yourself, it is to be a god to yourself because you are answerable to none but yourself for everything you do and this is what happened in the fall (Gen 3:5-6). The whole world however has been deceived in Adam because nobody is really answerable to only to himself, he in fact stands accountable to that ungodly peer pressure, which determines his survival in it. So, if you look at Rev 13:16-17 above, you understand that godless societies exude that unholy fear by which it’s members are forced to yield for the sake of their survival, because their members are mere existentialists, estranged from God, knowing nothing more than their own existence. God’s Law on the other hand was revealed to us men through Christ (Jn 1:18), which in the Old Testament was through the Angel of the Lord a.k.a. the Son of God and in the New Testament through Jesus Christ (Gal 3:19). This Law is the very nature of God, whose image we were made in and whose character we were made to represent in our being through in His Son Jesus Christ (Col 1:16-20). Now, what exactly is this Law?

Mat 22:36-40
36 Master, which is the great commandment in the law?
37 Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind.
38 This is the first and great commandment.
39 And the second is like unto it, Thou shalt love thy neighbour as thyself.
40 On these two commandments hang all the law and the prophets.

This is the Moral Law of God, whose interest we are to serve before our own. So, if you were to look at this in the context of the Ten Commandments in Exodus 20: 1-17, you would notice that this Law reflects the first four laws of the Ten Commandments instructing the Saints to fiercely love God with all their strength and second to love the people in our environment as ourselves. This Law as Jesus has taught us is not merely exercised in deed but also in thought (Job 31:1/Mat 5:17-20 & 27-28), which is metaphorically referred to as binding the Law to your forehead and right arm. Now if you were to take a look at the Ten Commandments, you will see what makes up the anti-Christian law, because Biblically a three time reference signifies fulfillment, so the number 6 representing the six laws to do with our neighbour, mentioned thrice i.e. 666, signifies an unsaved people (Rev 13:8) who are each a law to themselves. This is how a godless syndicate works in society, where neither grace nor deserving justice is entertained because surely you know what it is to be at the mercy of people and you know how senseless violence promotes that unholy fear by which these godless syndicates bring its people to remain committed to their cause for the sake of their own survival, being convinced by the awe in which they are brought to stand of ungodly syndicates who are recognized for their wickedness both in thought and deed (Rev 13:12-15).

Psalm 14:10
The fool has said in his heart, “There is no God.”
They are corrupt, they have committed abominable deeds;
There is no one who does good.

Psalm 84:10
For a day in Your courts is better than a thousand outside. I would rather stand at the threshold of the house of my God Than dwell in the tents of wickedness.

Mat 10
28 Do not fear those who kill the body but are unable to kill the soul; but rather fear Him who is able to destroy both soul and body in hell.

If we were to look at Ps 14:10 & Mat 10:28 in the light of Psalm 84:10, you would know how critical it is to remain devoted to God even in the face of affliction. If we were to look at the definition of Israel as given in Gen 32:28, we see God’s sovereignty in the salvation of His elect in this, that the godly are sanctified in the furnace of affliction which is the world, and prevail by the power of Christ… just as Shadrach, Meshack and Abednego did walking with the Son of God (Angel of the Lord) in the furnace of Nebuchadnezzar (Dan 3:25). The Church, which comprises of both New Testament and Old Testament saints is the spiritual Israel (Eph 2:11-13), that thrives by the Spirit of Christ even in the furnace of affliction. For Jesus is that seed of Abraham (Gal 3:16), which germinates in the hearts of God’s elect in calling them out of the world and adopting them into the family of God. This seed of Abraham, is the Spirit of Christ by whose power the individual who is called unto God, successfully resists the nature of fallen Adam, which is so naturally prevalent in the world that the Bible refers to it as that broad road of destruction (Mat 7:13). Surely this nature of fallen Adam is Satanic and resisting this nature (James 4:7) in the world is not to merely to fight against flesh and blood but to wage war against the spiritual forces or darkness (Eph 6:12) but as always there is hope for the elect in Christ, as mentioned in Rom 8:38-39. It was through the Son and for His glory that all creation came into being (Col 1:16), a glory which He shares with God the Father and God the Holy Spirit and it is through His Son that God promises a complete takeover of this world (Col 1:20/Dan 2:44-45). For there shall come a time when this world shall stop glorifying His good justice under the deception of the anti-Christ and be transformed to glorify His mercy and grace in Jesus Christ (Jn 3:16-18) as prophesied in Isaiah 11, for in this God delights, seeing His image restored in mankind by the redeeming power of His Almighty Son.

Happy Ending… (for the Godly)!