There are some certificates and diplomas from various schools, colleges, and training programs on my wall. Some say that they are just worthless pieces of paper. I disagree. The significance is not the paper, but what the paper represents. Each of them have the seal from the school, program, or organization that granted them. These certify that I have met the requirements necessary to receive the certification noted on that piece of paper.
There are other seals in our life that may serve similar purposes. Some of us wear uniforms with the seal of our organization. Some of us use items that have a "seal of approval" from some organization. Some of us may seal correspondence with wax and a stamp. All of these various kinds of seals serve similar purposes. In all cases, they identify or show genuineness. In some cases, such as the wax seal, they protect the contents from tampering.
According to the Bible, all of us who are Christians have a spiritual seal.
"And I saw another angel ascending from the rising of the sun, having the seal of the living God; and he cried out with a loud voice to the four angels to whom it was granted to harm the earth and the sea, saying, "Do not harm the earth or the sea or the trees until we have sealed the bond-servants of our God on their foreheads" (Rev 7:2-3).
All of God's faithful servants are sealed, which identifies them as belonging to God. This seal protects them from the plagues to come. For instance,
"Then out of the smoke came locusts upon the earth, and power was given them, as the scorpions of the earth have power. They were told not to hurt the grass of the earth, nor any green thing, nor any tree, but only the men who do not have the seal of God on their foreheads" (Rev 9:3-4).
This is similar to what happened during the Passover. The plague affected everyone who did not have the blood of the lamb on their door posts. Our Lord has "sealed" us, and that seal shows we belong to him and therefore are exempt from judgment and wrath.
The Bible also calls the Holy Spirit a "seal" (Eph 1:13). The Spirit identifies us as children of God who will inherit the Kingdom (Rom 8:9, 15-16), and helps us in our weaknesses (Rom 8:26; Eph 3:16).
You want a seal, not a mark (Rev 13:11-18). The mark represents what you receive as a result of compromise or accommodation of your faith. It is what you gain as the result of a divided allegiance. With the mark, you can "fit in" and not be a social misfit with the world. You can avoid the persecution, hardship, and ostracizing that comes because of your faith. However, those who have received the mark will suffer eternal torment in the end (Rev 14:9).
This is a warning not to compromise our faith, be intimidated, or be deceived. Jesus is Lord, not government, not cultural norms, not college professors, not your peers. Satan wants you to exchange your seal for a mark. Do not allow yourself to be intimidated or deceived.