It has been claimed that any sin will bring you out from under grace and you are now on your way to hell until you repent again. More specifically, the following lists of sin are typically used as benchmarks, sins that are sure to bring you out from under grace :
1 Cor 6:9 Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites,
10 nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God.
Gal 5:19 Now the works of the flesh are evident, which are: adultery, fornication, uncleanness, lewdness,
20 idolatry, sorcery, hatred, contentions, jealousies, outbursts of wrath, selfish ambitions, dissensions, heresies,
21 envy, murders, drunkenness, revelries, and the like; of which I tell you beforehand, just as I also told you in time past, that those who practice such things will not inherit the kingdom of God.
Rev 22:15 Outside are the dogs, those who practice magic arts, the sexually immoral, the murderers, the idolaters and everyone who loves and practices falsehood
In Acts 15, the apostles discuss what to do with the Gentiles who have taken up the faith, whether or not they should be taught to keep the whole law of Moses or not. They reject that idea and decide to write to them and tell them the following :
Acts 15:19 "It is my judgment, therefore, that we should not make it difficult for the Gentiles who are turning to God.
20 Instead we should write to them, telling them to abstain from food polluted by idols, from sexual immorality, from the meat of strangled animals and from blood.
21 For Moses has been preached in every city from the earliest times and is read in the synagogues on every Sabbath."
Presumably, the idea was that this was sufficient until someone arrived to teach them more about these things which again would be sufficient until the New Testament had been established, which would take another 50 years or so and even longer before all the books involved would circulate in all the churches.
The lists of sins mentioned in 15:19 basically involves sexual immorality and idolatry. These are important but the list is sorely lacking in relation to the lists of sins I quoted above. They mention that the law of Moses had been preached sufficently that even the Gentiles would have some rudimentory background for what its demands was and that would help but that doesn't mean that they would necessarily recall all the sins in the above lists, some of which are hardly mentioned in the law of Moses, at least not in terms of a concrete command not to do so.
So if avoiding those specific sins (or even any sin at all) was essential for continued salvation (until repenting later again) then the mentioned Gentiles had not been taught what was necessary for them to stay saved. They could commit sins they hadn't been taught about, die in the act then tell God that they had no idea. Which would render the apostle's council at Jerusalem, which is discussed favorably in the Bible, irresponsible. In fact, it would have been better for those Gentiles if they had been taught to simply keep the whole law of Moses (by the power of grace if you will) until they received further instructions and to repent as quickly as possible every time they misstepped while attempting to do that. That would have increased their chances of being saved into heaven enormously, given the "every time you sin you are no longer under grace until you repent again" doctrine.
The apostles' decision to "not make it difficult for the Gentiles that are turning to God" tells us a lot about how they viewed the power of grace to cover sin. Most posters here including myself believe that sin in a Christian's life has potential eternal consequences in that it undermines faith and shipwrecking faith brings you out from under grace but that usually takes time or a very severe act. These Gentiles were under Roman law and for them to avoid such things as murder, robbery and theft was a simple matter of teaching them to be generally lawabiding in terms of the laws of the land. Then they added avoiding idolatry and sexual immorality, none of which was illegal by Roman law, at least not in every form. That was rudimentory and sticking with that would probably keep them going until they gained a better understanding of the details.
The same is the case with many Christians in areas where it is difficult to be a Christian in the open, where Bibles are forbidden or hard to find. Some Chinese underground Christians had to make use of just having a few verses and some general understanding of the gospel. They had the Spirit but would that keep them alive since they didn't have any clear teaching on what specific list of sins would send them on their way to hell until repented of or in general, a lacking understanding of what is sin, to begin with ? Again, grace is more powerful than that.