What is predestinated in Romans 8 is
NOT salvation, but rather conformity to the image of Christ.
Rom 8:29 For whom he did foreknow, he also did predestinate to be conformed to the image of his Son [NOT "to be saved" or "to obtain eternal life", etc.], that he might be the firstborn among many brethren.
The image of Christ is the physical image of his resurrection body, a blessing connected to salvation but not salvation itself.
Romans 8 is saying that God predestinated foreknown believers to obtain a Christ-like resurrection body.
Please consider taking a few minutes to watch this Bible study:
29 For whom he foreknew, he also predestined to be like the image of his Son, that he might be the firstborn among many brethren.
30 But those whom He predestined, he called, and those whom He called, He justified; and those whom he justified, he glorified.
31 What can I say to this? If God is for us, who is against us?
(Rome.8:29-31)
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45 So it is written: the first man Adam became a living soul; and the last Adam is a life-giving spirit.
46 But not the spiritual first, but the spiritual, then the spiritual.
47 The first man is of the earth, a finger; the second man is the Lord from heaven.
48 As the finger is, so are the fingers; and as the heavenly is, so are the heavenly.
49 And as we have borne the image of the finger, so shall we bear the image of the heavenly one.
50 But I tell you, brethren, that flesh and blood cannot inherit the kingdom of God, and corruption does not inherit incorruption.
51 I tell you a secret: we will not all die, but we will all change
52 suddenly, in the twinkling of an eye, at the last trumpet; for it will sound, and the dead will rise incorruptible, and we will be changed.
53 For this corruptible must put on incorruption, and this mortal must put on immortality.
54 But when this corruptible thing is clothed with incorruption, and this mortal thing is clothed with immortality, then the written word will be fulfilled: death is swallowed up in victory.
55 Death! where's your sting? hell! where is your victory?
56 But the sting of death is sin, and the power of sin is the law.
57 Thanks be to God, who has given us victory by our Lord Jesus Christ!
58 Therefore, my beloved brethren, be firm, unshaken, always succeed in the work of the Lord, knowing that your labor is not in vain before the Lord.
(1 Corinthians 15: 45-58)
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6 If we say that we have fellowship with Him, but walk in darkness, then we are lying and do not act according to the truth;
7 But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus Christ his Son cleanses us from all sin.
8 If we say that we have no sin , we deceive ourselves, and the truth is not in us.
9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
10 If we say that we have not sinned, we make Him a liar, and his word is not in us.
(1 John.1:6-10)
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2 Beloved ones! we are now the children of God; but it has not yet been revealed what we will be. We only know that when it is revealed, we will be like Him, because we will see Him as He is.
3 And whosoever hath this hope in him purifies himself as he is pure.
4 Whosoever commits sin also commits iniquity; and sin is iniquity.
5 And you know that He came to take away our sins, and that there is no sin in him.
6 Whosoever abideth in him sinneth not; whosoever sinneth hath not seen him, nor known him.
7 Children! let no one deceive you. He who does the truth is righteous, just as He is righteous.
8 Whoever commits sin is of the devil, because the devil first sinned. For this purpose the Son of God appeared, to destroy the works of the devil.
9 Whosoever is born of God does not commit sin, because his seed abides in him; and he cannot sin, because he is born of God.
10 The children of God and the children of the devil are recognized in this way: Everyone who does not do righteousness is not of God, nor does he love his brother.
11 For this is the gospel which you have heard from the beginning, that we should love one another.,
12 Not like Cain, who was of the evil one, and killed his brother. Why did you kill him?" Because his works were evil, and his brother's works were righteous.
13 Do not be surprised, my brethren, if the world hates you.
14 We know that we have passed from death to life, because we love our brothers; he who does not love his brother remains in death.
15 Whosoever hateth his brother is a murderer; but ye know that no murderer hath everlasting life abiding in him.
16 We have known love in this, that he laid down his life for us: and we must lay down our lives for our brothers.
17 But whosoever hath abundance in the world, but seeth his brother in need, and shutteth his heart from him, how abideth the love of God in him?
18 My children! let us not love in word or in tongue, but in deed and in truth.
19 And this is how we know that we are of the truth, and we calm our hearts before Him.;
20 For if our heart condemns us, then God is greater than us, for God is greater than our heart, and knows all things.
21 Beloved ones! if our heart does not condemn us, then we have confidence in God,
22 And whatever we ask, we will receive from him, because we keep his commandments and do what is good in his sight.
23 But this is his commandment, that we believe in the name of his Son Jesus Christ, and love one another, as he has commanded us.
24 And he that keepeth his commandments abideth in him, and he in him. And that He abides in us, we know by the spirit that He has given us.
(1 John.3:2-24)
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So the point is that those who are like Christ, those who have His image, who have the image of His actions and His character, they are saved.