Think carefully about your answer for a bit: "How can we lose something we did nothing to gain?" In real life this happens all the time: someone gains an inheritance, or is given an anonymous gift, but they can just as quickly lose it! You ask a rhetorical question in an attempt to make a point, but your opening premise is faulty.
This is why my question is: Can anyone give a verse that states clearly "once saved always saved"?
The difference is that the unchanging GOD give the gift of free justification (rom 3.24.-25), free eternal life (Rom 6.23), and free salvation (eph 2.8-9) - HIS salvation to all who believe truly,
verses
'All that the Father gives to Me will come to Me, and him who comes to Me
I will in no wise cast out. For I am come down from Heaven not to do my own will, but the will of Him Who sent
Me. And this is the will of Him Who sent Me, that of all that He has given Me I should
lose nothing, but should raise it up at the Last Day,' (John 6.37-39)
But you do not believe (My Father's works) because you are not of My sheep. My sheep hear My voice and I know them, and they follow Me, and
I give unto them eternal life, and they shall
never perish, and none shall pluck them from My hand. My Father who gave them to Me is greater than all, and no one IS ABLE to pluck them out of the Father's hand. I and my Father are one (John 10.27-30).
All have sinned and come short of the glory of God, being
accounted as righteous by His grace FREELY through the redemption which is in Christ Jesus, Whom God has set forth to be a propitiation through faith by His blood (Rom 3,23-25).
'Even as the testimony of Christ was confirmed in you, so that you come behind in no gift, waiting for the revelation of our Lord Jesus Christ,
who will also confirm you unto the end, that you might be unreproveable in the Day of our Lord Jesus Christ.' (1 Corinth 1.6-8). (and this the corinthian church!)
'By grace you are saved, through faith, and that (gracious act) not of yourselves,
it is the gift of God and not of doings, lest any man should boast, for we are His workmanship, created in Christ Jesus unto good works, which God has before ordained that we should walk in them' (Eph 2.8-10).
'Being confident of this very thing, that
he which has begun a good work in you will perfect it until the day of Jesus Christ' (Phil 2.6).
'Who has saved us and called us with a holy calling, not according to our doings, but
according to His own purpose and grace, which was given us in Christ Jesus before the world began, but now has been manifested by the appearing of our Saviour, Christ Jesus, who abolished death and brought life and immortality to light through the Gospel (2 Tim 1.9).
I am not ashamed, for I know Him Whom I have believed, and am persuaded that
He is able to keep that which I have committed to Him against that Day (2 Tim 1.12).
But when the kindness of God our Saviour, and His love towards man appeared,
not by works done in righteousness which we did ourselves, but according to His mercy He saved us, through the washing of regeneration and renewing of the Holy Spirit, which He poured out upon us richly through Christ Jesus our Saviour, that being justified by His grace we might be made heirs according to the hope of eternal life. (Titus 3.4-7).
Wherein God, being minded to show more abundantly unto the heirs of promise
the immutability of His Counsel, interposed with an oath, that by two immutable things in which it is impossible for God to lie we may have a strong encouragement who have fled for refuge to lay hold of the hope set before us, which we have as an anchor of the soul, both sure and steadfast, and entering into that within the veil, whither as a forerunner Jesus entered for us, having become a High Priest for ever after the order of Melchisedek (Heb 7.7-20).
Wherefore He is able to
save to the uttermost them that come unto God by Him, seeing He ever lives to make intercession for them (Heb 7.25).
He has
perfected for ever those who are being sanctified (Heb 10.14)