For, him hath God, the Father, sealed. Since the son of man is referred to by Jesus in third person, he is not Jesus himself, as claimed by Christians. But Jesus was son of woman only, Virgin Mary, by virtue of what Christians celebrate as Immaculate Conception. They never refer to him by the common usage son of Adam i.e. son of man. The idea of son of man being sealed requires careful appreciation.
Seal has more than one meaning.
Firstly, it means closing off with wax, plastic tape, metal cap, door lock and the like to avoid any further filling, tampering or entering. By extension, it also means the last or ending material, action or event. The same denotations and connotations are equally true in Indo-European and other languages. Towards the end of his life came the very last of Qur'anic revelation. Bible corroborates this.