What sense and worth could there be if one truly received salvation and then truly lost it? Can it be rightly said that God can give “eternal salvation unto all them that obey Him” (Heb 5:9), while knowing they will eventually lose it? Such a situation would have no value at any time, but only confirms a misunderstanding of God’s omniscience. After rebirth, one will never conceive the desire against what He “works” within (Phl 2:13), which is “to desire and to perform of His good pleasure.” If those who profess faith in Christ cease to outwardly manifest the Christian walk, it confirms they have yet to be reborn.
It is this very “work” that keeps one from ever desiring to return to the former state of an unregenerate—which is “irrevocable” (Rom 11:29 - NKJV). If you’re reborn God will “keep you from evil” and “keep you from falling” (2Th 3:3; Jude 1:24), otherwise none could possibly remain in the faith; which answers to why salvation is permanent, and apostates (hypocrites) eventually manifest the absence of rebirth.
No matter who you are, there will always be a certain degree of misinterpretation of Scripture (concerning spiritual growth but not how to receive salvation), as it often presents statements that require researching beyond how a passage is given. This difficulty exists to confound the hypocrite (believers never cease from seeking truth), and admonish the saved to study; and without the use of at least one acceptable Bible commentator of your choice, there will always be a weighty time-lag in your learning progress.
"The Christian life is not our living a life like Christ, or our trying to be Christ-like, nor is it Christ giving us the power to live a life like His; but it is Christ Himself living His own life through us; 'no longer I, but Christ." -MJS