There are many teachings on the mark of the beast, but we must have the seal of God to gain entry into heaven. When satan’s army is unleashed that is known as the locust army they are commanded not to hurt those who have the seal of God in their foreheads. (Revelation 9:3,4). And there came out of the smoke locusts upon the earth: and unto them was given power, as the scorpions of the earth have power.And it was commanded them that they should not hurt the grass of the earth, neither any green thing, neither any tree; but only those men which have not the seal of God in their foreheads.
So what is this seal of God? When Nicodemus asked what must he do to be born again….John 3:3-8, he was hard pressed to understand that just as the wind blows where it will and cannot be seen yet we know it is there….so it is like when one is born again of the Spirit. Everyone around us does not see us as different or changed, yet our heart is set only on the Lord and we are different. For we are sealed by being given the Holy Spirit! (2 Corinthians 1:21,22). Now he which stablisheth us with you in Christ, and hath anointed us, is God;Who hath also sealed us, and given the earnest of the Spirit in our hearts.
We can go through out lives and hear the word of God, but not until we through genuine repentance does the truth make sense and our salvation becomes important. After we believe the truth we are sealed (In our minds-foreheads) and we are his. (Ephesians 1:13,14). In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.
The Lord knows those who are his! 2 Timothy 2:19.