Once saved always saved, vs
You can lose your salvation vs
You can walk away from your salvation.
Problem in understanding:
From God's perspective: Yes, once saved always saved.
From Man's perspective: We can appear to walk into and out of our security.
The real question: Are you really saved in the first place or are you currently in the midst of a long drawing process and only assume that you are saved?
The proof and evidense of salvation is systematically seen in perseverance. If God has actually, radically, once for all changed your life (new creation, old things passed away all things made new) then you will find that as time passes you will still be in Christ. Remoreful over sin, greatful to God, seeking to lift others up in prayer, trusting in God...
If you find that over a period of months or years passed, you are no longer concerned with God or the things of God as when you did at first then you may not have had the security that you once thought you did.
Salvation is of and from the Lord. We can't come in the first place unless we are called and drawn by the Father
through Christ, but many are called and few of the chosen.
Peter warns us to ensure our calling and election, Paul says in Rom 8:9 However, you are not in the flesh but in the Spirit,
if indeed the Spirit of God dwells in you. But
if anyone does not have the Spirit of Christ, he does not belong to Him.
God is faithful to complete the good work that He began in us until the day of Jesus' return. We must not be too quick to assume that the work has begun but instead "be all the more diligent to make certain about His calling and choosing you (read 1st Pet 1 for the things that we do to know.) Read 1st John.
If your life is the same as when you began with Christ, then worry.
If you find that over time your sin is systematically being replaced with Holiness, you are being made Godly, you love the Lord and have a better understanding of Him than at 1st, then praise God. But keep checking to make sure that you weren't mistaken.
Once saved always saved? From God's perspective no, so get in His perspective.