Regarding the oft-heard slogan, "Once Saved, Always Saved":
The Scripture uses the term "salvation" to mean the entire process involved in the Way of Life. The process begins with Justification by faith, necessitates Sanctification, and culminates in Resurrection; which is to say that Salvation is a process.
Those who have entered the Way of Life and are persisting in the pursuit of Sanctification are in the process of being saved. However, not everyone who enters the Way of Life perseveres in the Way unto the end, which is death.
A man cannot lose that which he does not possess. No man possesses Salvation until the day of the Resurrection; and once resurrected, a man cannot lose his Salvation. But at the present time, no one other than Christ Jesus has been resurrected from the dead, so no man has attained the status "once saved".
Moreover, the Resurrection is the process of birth of which Jesus spoke with Nicodemus, John 3:1-10. Resurrection is not simply re-animation; resurrection is a transformation whereby the mortal and corruptible creature of the Natural Realm is changed into an immortal and incorruptible being of the Spirit Realm. Not until the Resurrection may anyone rightly say that he has been "born again". At the present time, Christ Jesus alone has been born again; Jesus is the firstborn out from the dead, Colossians 1:18.