Comments on understanding "666"...
In ancient times, God said to keep the Law on your head and your hand at Deuteronomy 6:4-9...
"Listen, O Israel: Jehovah our God is one Jehovah. And you must love Jehovah your God with all your heart and all your soul and all your vital force. And these words that I am commanding you today must prove to be on your heart; and you must inculcate them in your son and speak of them when you sit in your house and when you walk on the road and when you lie down and when you get up. And you must tie them as a sign upon your hand, and they must serve as a frontlet band between your eyes; and you must write them upon the doorposts of your house and on your gates."
It was figurative. Basically, keep thinking about God's ways and let it influence all you do.
Six years work the land, the seventh is a sabbath rest.
Six days of work, the seventh day is a sabbath rest.
Six = Work
Seven = Rest
Revelation 14:11, the wild beast worshippers have "no rest".
Revelation 14:13, those in union with the Lord have "rest".
The visions of Revelation chapters 13 and 14 are parallel accounts. They are the same thing from a slightly different angle.
Once Jesus takes the throne in heaven, the Devil is cast down and permitted to rile up the UN to destroy all religious institutions. However, during that time true worshippers will keep relying on Jesus and allow God's ways to influence their decisions and actions. The UN will claim to be able to "work" without God to solve the earth's problems, but it won't work. True worshippers of God will recognize that no amount of "work" by humans alone can fix everything. They will "rest" in that they know only God can fix everything, and they will have confidence that at the end of the 3 1/2 year tribulation, Jesus will come just as he promised.
"666" = Work, work, work. No rest. No reliance on God. No real hope.
The context of Revelation 14:9,12 is after the great tribulation begins and the religious institutions have been destroyed...
"If anyone worships the wild beast and its image and receives a mark on his forehead or on his hand, he will also drink of the wine of the anger of God...Here is where it calls for endurance on the part of the holy ones, those who keep the commandments of God and hold fast to the faith of Jesus."
It will be imperative for true worshippers of God to maintain their hope and faith despite the crazy things going on during the great tribulation.
Our relationships with Jehovah and Jesus will be our place of rest. "Come to me, all you who are toiling and loaded down, and I will refresh you. Take my yoke upon you and learn from me, for I am mild-tempered and lowly in heart, and you will find refreshment for yourselves." (Matthew 11:28,29) "Jehovah God is my Shepherd...He refreshes me." (Psalm 23)
Many people who don't know anything about God or Jesus will need refreshment during the great tribulation. We will have the opportunity to refresh them by sharing with them the Only Source of hope and faith and life and peace and rest - Jehovah God through His Son Christ Jesus.