There are very clear warnings that Christians who commit certain things and fail to repent are in danger of being excluded from the Kingdom. ("Hell/outer darkness" issue aside)
The following verses are addressed directly to believers and are very plain.
Note: I will insert commentary in BLUE.
1 Corinthians 6:6-10
6 But brother goeth to law with brother, and that before the unbelievers.
7 Now therefore there is utterly a fault among you, because ye go to law one with another. Why do ye not rather take wrong? why do ye not rather suffer yourselves to be defrauded?
[Clearly not addressed to anyone but a believer.]
8 Nay, ye do wrong, and defraud, and that your brethren.
9 Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived:[who?] neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind,
10 Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God.
Galatians 5:19-21
19 Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness,
20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies,
21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.
[The they is simply "they". The verse is directed to Christians.]
Ephesians 5:1-7
1 Be ye therefore followers of God, as dear children;
2 And walk in love, as Christ also hath loved us, and hath given himself for us an offering and a sacrifice to God for a sweetsmelling savour.
3 But fornication, and all uncleanness, or covetousness, let it not be once named among you, as becometh saints;
4 Neither filthiness, nor foolish talking, nor jesting, which are not convenient: but rather giving of thanks.
[WHY?]
5 For this ye know, that no whoremonger, nor unclean person, nor covetous man, who is an idolater, hath any inheritance in the kingdom of Christ and of God.
6 Let no man deceive you with vain words: for because of these things cometh the wrath of God upon the children of disobedience.
7 Be not ye therefore partakers with them.
[Because if you partake with them you will get a portion with them!]
Luke 12:42-48
42 And the Lord said, Who then is that faithful and wise steward, whom his lord shall make ruler over his household, to give them their portion of meat in due season?
43 Blessed is that servant, whom his lord when he cometh shall find so doing.
44 Of a truth I say unto you, that he will make him ruler over all that he hath.
45 But and if that servant say in his heart,
[Same hypothetical servant. Still saved. Just behaving differently]
My lord delayeth his coming; and shall begin to beat the menservants and maidens, and to eat and drink, and to be drunken;
46 The lord of that servant will come in a day when he looketh not for him, and at an hour when he is not aware, and will cut him in sunder, and will appoint him his portion with the unbelievers.
47 And that servant, which knew his lord's will, and prepared not himself, neither did according to his will, shall be beaten with many stripes.
48 But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more.
