It is security of the believer if you stay with God in the truth if that is your desire to do so.
But a person can be in the faith, and saved, and fall away.
But you will say that will not happen to me which you are looking at it as a person cannot fall, but the Bible says that a person can fall away.
Rom 4:17 (As it is written, I have made thee a father of many nations,) before him whom he believed, even God, who quickeneth the dead, and calleth those things which be not as though they were.
Rev 13:8 And all that dwell upon the earth shall worship him, whose names are not written in the book of life of the Lamb slain from the foundation of the world.
Mat 25:34 Then shall the King say unto them on his right hand, Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world:
Luk 11:50 That the blood of all the prophets, which was shed from the foundation of the world, may be required of this generation;
God calls things that have not happened yet, as though they already happened, for if it is a plan of God to happen in the future it is the same as if it happened in the beginning, for it will surely come to pass with no hindrance.
Predestination does not mean God chooses who will saved without their choice, but it means God had the plan to give people salvation before He laid down the foundation of the world, so it is the same as if they have salvation in the beginning.
But this salvation is to whoever wants this salvation for we have a choice because God's kingdom is true love.
1Ti 4:10 For therefore we both labour and suffer reproach, because we trust in the living God, who is the Saviour of all men, specially of those that believe.
1Ti 2:3 For this is good and acceptable in the sight of God our Saviour;
1Ti 2:4 Who will have all men to be saved, and to come unto the knowledge of the truth.
2Pe 3:9 The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.
Rev 22:17 And the Spirit and the bride say, Come. And let him that heareth say, Come. And let him that is athirst come. And whosoever will, let him take the water of life freely.
God wants every person to be saved so why do they say He chooses who will be saved, and not saved without their choice.
Many are called, but few are chosen.
If God chooses who will be saved, and not saved, then why is He calling people that do not get saved.
We did not choose God but He chose us.
No person comes to the Son unless the Father draws them.
No person says Jesus is Lord but by the Holy Ghost.
1Co 1:26 For ye see your calling, brethren, how that not many wise men after the flesh, not many mighty, not many noble, are called.
When God calls a person according to their heart condition He will work in their life to get them to the truth, and when they get to the door of truth they have to decide to go through the door for His kingdom is true love, but they would of not gotten there if He did not intercede in the life.
And that truth is to accept Jesus as Lord and Savior, and to allow the Spirit to lead you to be Christlike which many people do not do that, and some people that started out doing that departed from the faith and went to doing worldly things.
Rom 11:20 Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear:
Rom 11:21 For if God spared not the natural branches, take heed lest he also spare not thee.
Rom 11:22 Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off.
Luk 9:62 And Jesus said unto him, No man, having put his hand to the plough, and looking back, is fit for the kingdom of God.
2Pe 2:20 For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.
2Pe 2:21 For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them.
2Pe 2:22 But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire.
1Ti 4:1 Now the Spirit speaketh expressly, that in the latter times some shall depart from the faith, giving heed to seducing spirits, and doctrines of devils.
New Age movement interpretation of the Bible that does not acknowledge Jesus as Lord and Savior, but evolved to be an ascended master.
These people that do this cannot be saved again if they change their mind.
So people can fall away if they go back to believing as the world, and enjoying sin.
The Bible says a Spirit led life will not fulfill the lusts of the flesh, for they have crucified the flesh with the affections and lusts.
Blessed is the person that endures temptation for when they are tried they shall receive the crown of life.
2 Ti 2:19 Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his. And, Let every one that nameth the name of Christ depart from iniquity.
2Ti 3:4 lovers of pleasures more than lovers of God;
2Ti 3:5 Having a form of godliness, but denying the power thereof: from such turn away.
2Ti 3:7 Ever learning, and never able to come to the knowledge of the truth.
Not every person that claims Christ walks through the door of truth so they were not saved in the first place.
And some were saved having faith and they went back to being worldly which they fell out of salvation which they can correct.
And if someone says it will always be corrected then there would not be warning about it like they will be cut off, and it would have been better if they did not know the truth than to depart from it.
The door of truth is to abstain from iniquity led by the Spirit but some never do that to begin with, and some did that but then went back to enjoying sin which they had faith and were saved but they lost security in salvation.
The Bible plainly states that if they escaped the pollutions of the world, and had the knowledge of the truth, and tasted of the heavenly gifts, but went back to sinning like a pig that goes back to being in the mud after it was clean then it would of been better if they had not known the truth than to turn away from it.
And after they are saved if they do not continue in the goodness of God they will be cut off.
1Co 10:12 Wherefore let him that thinketh he standeth take heed lest he fall.
Predestination means God already had the plan to give mankind salvation before He laid down the foundation of the world.
But this salvation is to whoever wants this salvation for God said He wants all people to come to repentance, and be saved, and is not willing that any perish.
And the Spirit and bride say come and any person that wants that salvation can have salvation.
Php 2:12 Wherefore, my beloved, as ye have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling.
They like to believe that a person cannot fall away because it gives them a relaxed attitude, and they can dabble in sin and cannot fall, but they take away the responsibility of the saint to make sure they behave Christlike led by the Spirit for the Spirit will not twist their arm to do it.
The Holy Spirit does not lead us unless we want that for if that were the case no person would ever sin again so we have to make the choice to want to do right before the Spirit will help us to do right.