Saying that unrepented grave sin sends someone to hell is not the same as saying that they have to earn their salvation, sorry. Nobody can earn salvation. God may permit you to throw it away, however, the same way a father can permit a son to separate himself from the family and walk away (cf the parable of the Prodigal Son).
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, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God. -- 1 Cor 6:9-10
Who said “unrepented”? When we accept Jesus as our saviour we repent of our sins and ask forgiveness. That’s not something we would do without the indwelling of the Spirit. When we accept Jesus as our Saviour we are indwelled with the Holly Spirit, thus the term “born again”. The sins that I once did I do not want to do any longer but not because of anything in my but from the Spirit within me.
People who talk so much about the works are putting the works before the saving. I’m putting the works after the saving as it should be. If it weren’t then we would be able to “boast” about what we did.