This is not what logic dictates. All those in Noah's Ark will be saved. If someone left the ark when the float waters came, too bad for them; they are not saved because they were once in the ark, for in the moment of truth, they were out of the ark. This is what logic dictates.
The definition of "in" that you are asserting is that once in, no one can ever get out OR they were never in to begin with. This is most illogical. See Post Hoc.
That explanation is out of context.
The context of salvation is not one that a person can walk out of. Who can walk out of eternity? No one except Christ. This is the correct context and definition.
If it is no longer the person who lives, but Christ who lives in them...the logic that you have just presented would mean Jesus could give up His eternal life, for it would be Him walking out of the eternity that He Himself made eternal by His own life. In which there is no logic at all, except that to believe that such a thing were even possible, is
not to have understood the definition of the salvation of Christ to be
His eternal life given to those whom He enters into.
The point is...there are no conditions put upon Christ Himself, except those He has already fulfilled.
What then of ongoing sin by those who have died to self in whom it is no longer they who lives but Christ who lives in them?
The answer is that just as the error of defining the salvation of Christ not as eternal as Christ is eternal, the definition of ongoing sin is in error. Indeed, one lie requires more lying to maintain it.
What then is that error of defining ongoing sin--put upon Christ in who there is no sin? It is not having the understanding that with Christ comes eternity. Which is the error of wrongfully placing the mark of the End, according to the flesh, rather than according to the Spirit. And not believing that Christ is that End--just as He said.
Some of you need to examine your own selves, and what you do and do not believe that is written. Part of the scriptures is not all truth, but all must be reconciled, and this you have not done.