A Christian is sealed by his baptism; his works will be judged according to the Christian law. Of course his works lead him to sin and repentance many times; but sealed he remains, as whatever he does he is a Christian.
Likewise, confirmation and Holy Orders supply seals specific to their particular charisms.
You are confusing the seal with the state of grace. It is not the same thing.
My impression of "sealing" in the Bible is of something permanent. Here, it looks like you are saying that the only thing that is permanent is that the person can call himself a Christian, whether he winds up in heaven or hell. Why is this of any value, if a number of Christians go to hell?