The Mark of the beast[666] is merely Man trying to get to God his way, rejecting the way of the God's appointed means, through the electing Grace of God in Christ Jesus, the Lamb slain from the foundation.
This was first seen in cain, of whom at his birth eve says:
gen 4:
1And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten
a man from the LORD.
The mark is the number of a man rev 13:18
Here is wisdom. Let him that hath understanding count the number of the beast:
for it is the number of a man; and his number is Six hundred threescore and six.
Its that spirit in the unregenerated man that as cain did, who thought his way which was the right way to approach God in the best he could offer and so proverbs tells us prov 14:12
There is a way which
seemeth right unto a man, but the end thereof are the ways of death.
prov 16:25
There is a way
that seemeth right unto a man, but the end thereof are the ways of death.
Hence it is that broad way that leadeth to destruction
Matt 7:13
Enter ye in at the strait gate: for wide is the gate,
and broad is the way, that leadeth to destruction, and many there be which go in thereat:
cain started this way, its the way of man without Christ...