It is written..."For both he that sanctifieth and they who are sanctified are all of one: for which cause he is not ashamed to call them brethren," (Heb 2:11)
"By the which will we are sanctified through the offering of the body of Jesus Christ once for all."
(Heb 10:10)
"For by one offering he hath perfected for ever them that are sanctified." (Heb 10:14)
"Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace?" (Heb 10:29)
Not one of those verses imposes a gradual sanctification, knowing that which sanctifies us is the blood of Christ, which has already been applied to the repentant at our "immersion" into Jesus' death.
The unsanctified are not yet atoned for, and Jesus has yet to call them "brethren".
They are the ones who "walk away".