So if someone turns away from God, after having been justified, living a life of sin, are they still justified/saved?
Yup. According to God they are.
We don't know that the experience of heaven is the same for all and I think God's Word shows that it will not be.
They are missing out on a lot of the rewards and crowns that Jesus will be giving in heaven when all we have done on earth is evaluated by fire.
1 Corinthians 3:11-14
For no man can lay a foundation other than the one which is laid, which is Jesus Christ. Now if any man builds on the foundation with gold, silver, precious stones, wood, hay, straw, each man's work will become evident; for the day will show it because it is to be revealed with fire, and the fire itself will test the quality of each man's work.
Matthew 5:12
"Rejoice and be glad, for your reward in heaven is great; for in the same way they persecuted the prophets who were before you.
Luke 6:23
"Be glad in that day and leap for joy, for behold, your reward is great in heaven For in the same way their fathers used to treat the prophets.
Revelation 22:12
"Behold, I am coming quickly, and My reward is with Me, to render to every man according to what he has done.
Philippians 3:14
I press on toward the goal for the prize of the upward call of God in Christ Jesus.
Hebrews 11:26
considering the reproach of Christ greater riches than the treasures of Egypt; for he was looking to the reward.
Matthew 16:27
"For the Son of Man is going to come in the glory of His Father with His angels, and WILL THEN REPAY EVERY MAN ACCORDING TO HIS DEEDS.
Daniel 12:3
"Those who have insight will shine brightly like the brightness of the expanse of heaven, and those who lead the many to righteousness, like the stars forever and ever.
Luke 19:15-19
"When he returned, after receiving the kingdom, he ordered that these slaves, to whom he had given the money, be called to him so that he might know what business they had done. "The first appeared, saying, 'Master, your mina has made ten minas more.' "And he said to him, 'Well done, good slave, because you have been faithful in a very little thing, you are to be in authority over ten cities.'
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1 Corinthians 3:8
Now he who plants and he who waters are one; but each will receive his own reward according to his own labor.
2 Corinthians 9:6
Now this I say, he who sows sparingly will also reap sparingly, and he who sows bountifully will also reap bountifully.
Matthew 5:10-12
"Blessed are those who have been persecuted for the sake of righteousness, for theirs is the kingdom of heaven. "Blessed are you when people insult you and persecute you, and falsely say all kinds of evil against you because of Me. "Rejoice and be glad, for your reward in heaven is great; for in the same way they persecuted the prophets who were before you.
Luke 6:22-23
"Blessed are you when men hate you, and ostracize you, and insult you, and scorn your name as evil, for the sake of the Son of Man. "Be glad in that day and leap for joy, for behold, your reward is great in heaven For in the same way their fathers used to treat the prophets.
1 Peter 5:4
And when the Chief Shepherd appears, you will receive the unfading crown of glory.
1 Thessalonians 2:19
For who is our hope or joy or crown of exultation? Is it not even you, in the presence of our Lord Jesus at His coming?
2 Timothy 4:8
in the future there is laid up for me the crown of righteousness, which the Lord, the righteous Judge, will award to me on that day; and not only to me, but also to all who have loved His appearing.
Ephesians 2:6
and raised us up with Him, and seated us with Him in the heavenly places in Christ Jesus,
John 14:3
"If I go and prepare a place for you, I will come again and receive you to Myself, that where I am, there you may be also.
John 17:24
"Father, I desire that they also, whom You have given Me, be with Me where I am, so that they may see My glory which You have given Me, for You loved Me before the foundation of the world.