Tell me if this is correct:
No matter what sin you commit, even if someone had sold their soul to the devil, they could be forgiven for this or any other act no matter what? On the terms that they repent and ask forgiveness, could they still go to heaven?
The potential forgiveness is always there, but God warns us that because the nature of certain sins, those who commit them are unlikely to change (repent) and ask God forgiveness.
""Therefore I will judge you, O house of Israel, every one according to his ways," says the Lord GOD. "Repent, and turn from all your transgressions, so that iniquity will not be your ruin. Cast away from you all the transgressions which you have committed, and get yourselves a new heart and a new spirit. For why should you die, O house of Israel? For I have no pleasure in the death of one who dies," says the Lord GOD. "Therefore turn and live!"" (Ezekiel 18:30-32).
"For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame" (Hebrews 6:4-6).
"For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins, but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries" (Hebrews 10:26-27).
If you sincerely want to please the Lord your God and are willing give up worldly living in order to do what God wants, God will not turn you away. "The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance" (II Peter 3:9). But you must be willing to approach God on His terms and not your own. "For do I now persuade men, or God? Or do I seek to please men? For if I still pleased men, I would not be a bondservant of Christ" (Galatians 1:10).
I suspect many cling to the myth that some sins cannot be forgiven to write themselves an excuse for not even trying to please God. Don't be one of them.