Allah Almighty is the most merciful. He says anyone who seeks forgiveness from sin while they’re alive breathing, they are Well, they will be forgiven, no matter what the sin is.
There is one sin that is considered the worst possible sin that man could commit according to the Quran and the teachings of the Prophet salallahu alaihe wasalam, this sin is Known as shrik, shrik meaning to worship Someone besides Allah or with Allah subhanahu wa’ta’ala Association of partnership with Allah, Allah subhanahu wa’ta’ala states that He will not forgive shirk under certain circumstances.
If a person has committed shirk in their lives and they seek forgiveness from they will definitely be forgiven without a shadow of doubt.
The only time He doesn’t forgive shirk according to Him is if you died and you did not repent from your sins.
If you want to achieve comfort in any situation don’t insult people, don’t abuse them. You disagree, express that disagreement with utmost respect, respect yourself to begin with and then respect others.
If you really care for mankind and you really care for people and want them to see the truth, the truth will never be communicated to them via insult and abuse rather it will be done in a very respectful manner that is convincing.