In the end, the sealing power will come into play. Benjamin said, "I would that ye should be steadfast and immovable, always abounding in good works, that Christ, the Lord God Omnipotent, may seal you his, that you may be brought to heaven, that ye may have everlasting salvation and eternal life, through the wisdom, and power, and justice, and mercy of him who created all things, in heaven and in earth, who is God above all (Mosiah 5:15)." This conclusion to Benjamin’s speech is a truly beautiful, prophetic blessing upon all his people, ending with the sealing, the placing of the Lord’s seal of approval that binds us to him.
What did an ancient seal look like? It was like an official stamp. It could be a cylinder seal which parties to an official document or contract would roll on clay. It was, in a way, like a credit card. It was the ancient world’s way of putting a stamp of approval on a transaction. So, when the Lord seals us his, it is as if he is putting his seal, his signature on us.
When a person in the ancient Roman world was purchased as a slave, they would brand their foreheads somewhat like branding cattle. If slaves belonged to a temple and were dedicated as temple servants, they could have the seal or the brand of the temple, so the people knew to whom they belonged. While this was not done in ancient Israel, as far as we know, Benjamin had talked earlier about people "serving" God, and that could have included temple servants or people devoted to the Lord in his sacred house.
Benjamin also told his people that, by making this covenant, they had now become sons and daughters of Christ. As sons and daughters, they were free persons, and they were entitled to inherit from the Father. They now belonged to him in that sense, and they were now spiritually reborn and begotten into the family. With this formality completed for each of us, life has just begun. A new life is now lies ahead.
Book of Mormon Central, "How Does Christ ‘Seal You His’ (Mosiah 5:15)," KnoWhy 558 (April 21, 2020).