It isn't.
We use this Scripture.
Some things for you to consider and to know why I know that I will never lose my salvation.
Jesus promised that I cannot lose my salvation:
All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out. (John 6:37)
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, neither shall any man pluck them out of my hand.
My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand. (John 10:27-29)
Further, that I cannot do anything to lose my salvation because:
Salvation is by grace through faith, and not by works. It is a gift from God. No man can lose his salvation on his own, because no man earned his salvation.
For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
Not of works, lest any man should boast. (Ephesians 2:8-9)
If I had to do anything to earn or keep my salvation, I would easily lose it.
For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the book of the law to do them. (Galatians 3:10)
For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all. (James 2:10)
Yet 2 Timothy assures us it is Jesus Christ who keeps us, not we ourselves.
For the which cause I also suffer these things: nevertheless I am not ashamed: for I know whom I have believed, and am persuaded that he is able to keep that which I have committed unto him against that day.
(2 Timothy 1:12)
Galatians 2:21 states clearly that if we could become righteous by anything we do, then Jesus Christs death was in vein.
I do not frustrate the grace of God: for if righteousness come by the law, then Christ is dead in vain.
(Galatians 2:21)
God wont cast me out, no man can cause me to lose my salvation, I cannot lose it myself and there is nothing else to make me lose my salvation
For I am persuaded, that neither
death, - you cannot lose it when you die
nor life, - you cannot lose it while youre alive
nor angels, - cannot take it away from you
nor principalities, - the government cant take it from you.
nor powers, - the devil cannot cause you to lose it.
nor things present, - nothing happening right now
nor things to come, - nothing happening in the future.
Nor height, - nothing above you.
nor depth, - nothing below you.
nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord. (Romans 8:38-39)
Does this mean I can go on and knowingly sin? Absolutely not!
What then? shall we sin, because we are not under the law, but under grace? God forbid. (Romans 6:15)
But how I serve the Lord while here on earth will be judged.
Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.
If any man's work abide which he hath built thereupon, he shall receive a reward.
If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire. (1Corinthians 3:13-15)