Assalamu Alaikum,
My dear sister Islam is not only about outward actions but in fact the state of our hearts and the inner self is of huge importance:
The Prophet (Sallalahu alaihi Wasallam) said: The faith of a servant is not upright until his heart is upright, and his heart is not upright until his tongue is upright. A man will not enter Paradise if his neighbor is not secure from his evil.(Ahmed)
Every single one of our good actions will be judged due to the intentions behind them and whether or not we did them sincerely for the sole pleasure of Allah or whether we did them to "show off" and to please other people so people can look up to us and praise us. We will all be asked on the day of judgement regarding our actions and the intentions behind them and whether we did them sincerely for his pleasure or not:
The Prophet (Sallalahu alaihi Wasallam) said: Verily, the people will be raised for judgment only according to their intentions.(Ibn Majah)
The Prophet (Sallalahu alaihi Wasallam) also said: "Deeds are but by intentions and every person shall have what he intended. Thus, whose migration was for the sake of Allah and His Messenger, then his migration was for Allah and His Messenger. And whose migration was for the sake of some worldly benefit or marrying some woman, then his migration was for what he migrated." (Al-Bukhari)
Throughout the Qur'an you will come across references towards the hypocrites who are those whom they claim to have true faith and show people that they do good actions and they speak very elequontly but they have corrupted hearts and they do not truly believe and behind closed doors they plan and plot against the Muslims and befriend the enemies of Islam. Therefore Allah sees all that we do by action as well as what our hearts intend by it and whether we are sincere:
Allah said: And We shall turn to the deeds they have done and scatter them like dust.(Qur'an 25;23)
Regarding good manners, character and behaviour then this has huge significance in our lives as the Prophet (Sallalahu alaihi Wasallam) came to us to perfect our characters:
The Prophet (Sallalahu alaihi Wasallam) said: Verily, I have only been sent to perfect righteous character. (Aḥmad)
The Prophet (Sallalahu alaihi Wasallam) said: “Nothing is heavier upon the scale of the believer on the Day of Resurrection than good character. Verily, Allah hates the vulgar, obscene person.” (Al-Tirmidhi)
The Prophet (Sallalahu alaihi Wasallam) said: "The Muslim is the one from whose tongue and hand the people are safe, and the believer is the one people trust with their lives and wealth. (Al Nasai)
Having good character and manners surpasses others in good actions:
Ibn al-Qayyim (Ra) writes: The religion itself is entirely good character, so whoever surpasses you in character has surpassed you in religion. (Madārij al-Sālikīn 2/294)
So we must leave it to Allah to judge the state of a person's heart and inner self and know that he is the most just. He will never wrong any soul to even a single atoms worth of injustice. If anyone wronged has us then he is fully aware of it and justice will be done if not in this world then the next or even both. Of course it is far better to forgive as Allah is especially towards those who forgive others:
“. . . and let them pardon and overlook. Would you not like that Allah should forgive you? And Allah is Forgiving and Merciful.” [Quran 24:22]
If our disputes with one another are not resolved in this world then they will surely be resolved in the next.
A typical objection shaythan gives us regarding those non Muslims who seemingly have good hearts and actions is that why would Allah make them burn in Hell forever? However firstly it is not our decision to make who goes to Hell and who goes to Paradise. Secondly we do not know the state of anyone's heart nor do we know what they do in private. Our criterion is based on a snippet of another person's life and on our emotions. However our knowledge is very narrow, limited and finite whereas Allah's knowledge is all encompassing and infinite.
Therefore we leave the decision of the fate of every single soul to the one who created us and who knows our inwardly and outwardly actions from the beginning of our lives to the very end. So we must worry for ourselves and our families and the state of our Ummah rather than to condemn others to Hell or give glad tidings to people of Paradise which is not within our knowledge and authority to do so. Instead we must focus on fulfilling our obligations unto Allah and continuously improving ourselves, correcting our hearts, characters and manners.
When it comes to Non believers then we should be good examples to them so that they may become attracted to our Deen and we should invite them to the truth with wisdom and tact and know that guidance is not in our hards. Whatever the outcome will be on the day of Judgement then know that Allah is the best Judge and the most just and he will never wrong any soul:
Allah said: Indeed, Allah does not wrong the people at all, but it is the people who are wronging themselves.(Qur'an 10;44)