Law of First Mention: Gen_4:15 And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him.
Also, have a look at the word in Greek for yourself in Revelation. It’s a mark like ... a real mark.
Knowing what we know about technology today, the mark of the beast, might be a computer chip of some sort. We simply don’t know for sure, but I am 💯% sure it is NOT Sunday worship. That is just pure, unadulterated horse hockey.
What the book of Revelation starts with r.e. "the mark" is first a 3 “Do not harm the land or the sea or the trees until we put a seal on the foreheads of the servants of our God. -- the seal on the foreheads of the servants of Our God - the Tau, or sign of the Cross
And in that we read about the lamb of God
Later we see Satan's jealousy and how Satan tries to denigrate God -- we read about the evil mark and then the parody of the lamb (which comes from the land and is a symbol of the Sanhedrin)
In the same way Satan tries to denigrate God's kingdom - as we see in the satanic concept of the pre-tribulation rapture and dispensationalism.