1. What is the Mark?
Many believers (and others) associate the Mark of the Beast with the mysterious number 666, and they endeavor to calculate its meaning, as if doing so will put an end to the coming of the Beast or of the end-times. It won't.
By focusing on this numerology, many stay puzzled and confused. They remain distracted ("look over here") while the true Mark of the Beast takes its toll. The reality is that the Mark of the Beast is not necessarily visible. You don't need to tattoo "666" onto your forehead or hand in order to take this Mark. Neither is any imprinted logo or stamp, or implanted identity chip, necessary to be so marked. While such a worldwide phenomenon may come about in the future, such are less worrisome than the heart of the matter, that the more dangerous Mark of the Beast is spiritual rot, that is, corruption.
It is therefore not necessary to discover which device is going to enslave mankind. Instead, we must find out why free men surrender to such evil devices. Only then can we begin to fight spiritual descent.
The key to all of this is simple, actually. We merely need to guard against any promises or false hopes which cause us to veer away from God. Easier said than done, however.
When evil makes promises, they are attractive promises. Satan offered Jesus food, then safety, and finally great power (Matthew 4:1-11), but Christ could not be moved. He rejected Satan, thus rejecting the Mark of the Beast. How did Jesus accomplish this? By invoking the Word of God. But not only this, for He also fasted to the brink of death. In other words, Jesus would rather have died than succumb to evil offerings of delicious sustenance, personal security, and elite monarchy. Christ instead chose God for sustenance, security, and a feeling of power.
Like Christ, we need to arm and shield ourselves with the Word of God, and live in such righteousness, a mix of intense godliness and fierce integrity, so that when the time comes we will be prepared to rebuff the Mark of the Beast.