Inhabiting the Kingdom is not the issue...those in Christ are already transferred there. But inheriting the Kingdom, evidently meaning a position of service and authority there, appears to be earned or lost here and now depending on how we run this race.
Nope - the kingdom: eternal life, is...the issue.
Specifically, the conduct of the possessor of said inheritance: of eternal life; in contrast to the conduct of the lost.
Acts 26:17 Delivering thee from the people, and from the Gentiles, unto whom now I send thee, 26:18 To open their eyes, and to turn them from darkness to light, and from the power of Satan unto God, that they may receive forgiveness of sins, and inheritance among them which are sanctified by faith that is in me.
2 Corinthians 4:3 But if our gospel be hid, it is hid to them that are lost: 4:4 In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
Said light? The love of God for us in His Son, by the Cross...
Romans 5:5 And hope maketh not ashamed; because the love of God is shed abroad in our hearts by the Holy Ghost which is given unto us. 5:6 For when we were yet without strength, in due time Christ died for the ungodly. 5:7 For scarcely for a righteous man will one die: yet peradventure for a good man some would even dare to die. 5:8 But God commendeth his love toward us, in that, while we were yet sinners, Christ died for us.
In contrast...
1 Corinthians 6:9 Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind, 6:10 Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God. 6:11 And such were some of you: but ye are washed, but ye are sanctified, but ye are justified in the name of the Lord Jesus, and by the Spirit of our God.
6:19 What? know ye not that your body is the temple of the Holy Ghost which is in you, which ye have of God, and ye are not your own?
6:20 For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God's.
The bought with a price is the only reward he mentions there, by the way - the reward of eternal life.
It's basically...
Romans 6:16 Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness? 6:17 But God be thanked, that ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you. 6:18 Being then made free from sin, ye became the servants of righteousness. 6:19 I speak after the manner of men because of the infirmity of your flesh: for as ye have yielded your members servants to uncleanness and to iniquity unto iniquity; even so now yield your members servants to righteousness unto holiness. 6:20 For when ye were the servants of sin, ye were free from righteousness. 6:21 What fruit had ye then in those things whereof ye are now ashamed? for the end of those things is death. 6:22 But now being made free from sin, and become servants to God, ye have your fruit unto holiness, and the end everlasting life. 6:23 For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.
At the same time, he no more goes into the reward of said inheritance there, than he does in Romans 6.
And Corinthians is based on the doctrine later laid out in more detail, in Romans.
"The reward of the inheritance" (the issue of rewards) is an issue different from the issue of "inherit the kingdom" (the issue of eternal life).
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Note:
Corinthians is "reproof" of behavior not in line with the "doctrine" or instruction in righteousness" (2 Tim. 3:16,17) merely laid out in more detail, later in Romans.
Just as Galatians (also written way before Romans) is "correction" of belief not in line with the "doctrine" or instruction in righteousness" (2 Tim. 3:16,17) later laid out in more detail, in Romans.
(As in Romans itself; evident throughout both Galatians and the two Corinthians Epistles, is that Paul had long taught and preached much of the basic material in Romans and Ephesians, long before he wrote either of those two later writings).
Rom. 5:8