John 5:24 would teach us that (in a sense) initial salvation is final salvation...that upon believing we pass from death into everlasting life.
If one is initially saved eternally, then nothing can take salvation away; otherwise it isn't eternal, it is temporal.
Yes, it is one of the John 3:16 type of verses,
which we know is nonsense because it doesn't
specify what kind of belief is necessary,
e.g. it doesn't rule out simple intellectual belief,
which most kids have in Sunday School, right?
IMO, these types of verses are the little hooks
used to catch the unsuspecting little fishes!
They offer nothing but hope, confidence, optimism, etc.
Later, the Holy Spirit tries to illuminate these little fishes with deeper
understanding about what's involved over time as they grow and learn, etc.
What dost thou thinkest about "counting the cost" of following Jesus
... (before really getting started?)?
.