I was not raised KJVO or OSAS because I had a nominal Christian mother and an agnostic father. I was not saved until rather late in life, so you can't use that argument on me (which I think means nothing anyway in re to this issue).
Believers are seated in the heavenly places - now!
4But God, being rich in mercy, because of His great love with which He loved us,
5even when we were dead in our transgressions, made us alive together with Christ (by grace you have been saved),
6and raised us up with Him, and seated us with Him in the heavenly places in Christ Jesus, 7so that in the ages to come He might show the surpassing riches of His grace in kindness toward us in Christ Jesus. Eph. 2
Believers are of God's household:
19So then you are no longer strangers and aliens, but you are fellow citizens with the saints, and are of God's household,
20having been built on the foundation of the apostles and prophets, Christ Jesus Himself being the corner stone, Eph. 2
Believers have a deposit or guarantee - the Holy Spirit is our "pledge," a pledge from God! This means a promise by God. God does not break his pledges.
13In Him, you also, after listening to the message of truth, the gospel of your salvation--having also believed, you were sealed in Him with the Holy Spirit of promise,
14who is given as a pledge of our inheritance, with a view to the redemption of God's own possession, to the praise of His glory.
Eph. 1
We are saved for God's glory, not for ourselves. I think believing we can lose our salvation is a focus on man, not on God. Since we are saved by God's mercy and power and nothing of our own, neither can be break what God has done.