Salam
I hear people say inward Shirk is forgivable unlike outward Shirk, but this is false. First the motivation for outward Shirk and reason why it's condemned is because of inward Shirk.
وَقَالَ إِنَّمَا اتَّخَذْتُمْ مِنْ دُونِ اللَّهِ أَوْثَانًا مَوَدَّةَ بَيْنِكُمْ فِي الْحَيَاةِ الدُّنْيَا ۖ ثُمَّ يَوْمَ الْقِيَامَةِ يَكْفُرُ بَعْضُكُمْ بِبَعْضٍ وَيَلْعَنُ بَعْضُكُمْ بَعْضًا وَمَأْوَاكُمُ النَّارُ وَمَا لَكُمْ مِنْ نَاصِرِينَ | He said, ‘You have taken idols [for worship] besides Allah for the sake of [mutual] affection amongst yourselves in the life of the world. Then on the Day of Resurrection you will disown one another and curse one another, and the Fire will be your abode, and you will not have any helpers.’ | Al-Ankaboot : 25
Really, this verse is saying outward Shirk was due to love of affection type amongst themselves, it was a means to unite them.
Furthermore it's impossible to truly believe in God and not do good deeds. It's possible the mind is convinced of Islam, but the heart to be convinced of God would fear God and obey him, otherwise, it's a deception:
وَلَا تَأْكُلُوا مِمَّا لَمْ يُذْكَرِ اسْمُ اللَّهِ عَلَيْهِ وَإِنَّهُ لَفِسْقٌ ۗ وَإِنَّ الشَّيَاطِينَ لَيُوحُونَ إِلَىٰ أَوْلِيَائِهِمْ لِيُجَادِلُوكُمْ ۖ وَإِنْ أَطَعْتُمُوهُمْ إِنَّكُمْ لَمُشْرِكُونَ | Do not eat [anything] of that over which Allah’s Name has not been mentioned, and that is indeed transgression. Indeed the satans inspire their Awliya to dispute with you; and if you obey them then you are polytheists. | Al-An'aam : 121
Furthermore Quran has condemned desiring the life of this world:
مَنْ كَانَ يُرِيدُ الْحَيَاةَ الدُّنْيَا وَزِينَتَهَا نُوَفِّ إِلَيْهِمْ أَعْمَالَهُمْ فِيهَا وَهُمْ فِيهَا لَا يُبْخَسُونَ | As for those who desire the life of this world and its glitter, We will recompense them fully for their works therein, and they shall not be underpaid in it. | Hud : 15
أُولَٰئِكَ الَّذِينَ لَيْسَ لَهُمْ فِي الْآخِرَةِ إِلَّا النَّارُ ۖ وَحَبِطَ مَا صَنَعُوا فِيهَا وَبَاطِلٌ مَا كَانُوا يَعْمَلُونَ | They are the ones for whom there shall be nothing in the Hereafter but Fire: what they had accomplished in the world has failed, and vain/false what they use to do. | Hud : 16
Furthermore Quran has described that it's only those who worship Satan with God that Satan has control over:
فَإِذَا قَرَأْتَ الْقُرْآنَ فَاسْتَعِذْ بِاللَّهِ مِنَ الشَّيْطَانِ الرَّجِيمِ | When you recite the Quran, seek the protection of Allah against the outcast Satan. | An-Nahl : 98
إِنَّهُ لَيْسَ لَهُ سُلْطَانٌ عَلَى الَّذِينَ آمَنُوا وَعَلَىٰ رَبِّهِمْ يَتَوَكَّلُونَ | Indeed he does not have any authority over those who have faith and put their trust in their Lord. | An-Nahl : 99
إِنَّمَا سُلْطَانُهُ عَلَى الَّذِينَ يَتَوَلَّوْنَهُ وَالَّذِينَ هُمْ بِهِ مُشْرِكُونَ | His authority is only over those who give mastery to him and those who make him a partner [of Allah]. | An-Nahl : 100
That means if we believe in God and rely on him, Satan has no authority over us and we will defeat his attempts of controlling us.
Furthermore Quran shows outward belief is not good enough, so inward Shirk is not forgivable:
يَوْمَ تَرَى الْمُؤْمِنِينَ وَالْمُؤْمِنَاتِ يَسْعَىٰ نُورُهُمْ بَيْنَ أَيْدِيهِمْ وَبِأَيْمَانِهِمْ بُشْرَاكُمُ الْيَوْمَ جَنَّاتٌ تَجْرِي مِنْ تَحْتِهَا الْأَنْهَارُ خَالِدِينَ فِيهَا ۚ ذَٰلِكَ هُوَ الْفَوْزُ الْعَظِيمُ | The day you will see the faithful, men and women, with their light moving swiftly in front of them and on their right, [and they are greeted with the words:] ‘There is good news for you today! Gardens with streams running in them, to remain in them [forever]. That is the great success.’ | Al-Hadid : 12
يُنَادُونَهُمْ أَلَمْ نَكُنْ مَعَكُمْ ۖ قَالُوا بَلَىٰ وَلَٰكِنَّكُمْ فَتَنْتُمْ أَنْفُسَكُمْ وَتَرَبَّصْتُمْ وَارْتَبْتُمْ وَغَرَّتْكُمُ الْأَمَانِيُّ حَتَّىٰ جَاءَ أَمْرُ اللَّهِ وَغَرَّكُمْ بِاللَّهِ الْغَرُورُ | They will call out to them, ‘Did we not use to be with you?’ They will say, ‘Yes! But you cast yourselves into perdition. You awaited and were skeptical, and [false] hopes deceived you until the edict of Allah came, and the Deceiver deceived you concerning Allah. | Al-Hadid : 14
فَالْيَوْمَ لَا يُؤْخَذُ مِنْكُمْ فِدْيَةٌ وَلَا مِنَ الَّذِينَ كَفَرُوا ۚ مَأْوَاكُمُ النَّارُ ۖ هِيَ مَوْلَاكُمْ ۖ وَبِئْسَ الْمَصِيرُ | So today no ransom shall be taken from you or the faithless. The Fire will be your abode: it is your [ultimate] refuge and an evil destination.’ | Al-Hadid : 15
This also verified in words of Imam Jaffar (a) in Misbahal Shariah:
Do not show off your actions to someone who neither gives life nor causes death, and who cannot take away from you your burdens. Showing off is a tree whose only fruit is hidden association of other gods with Allah, and its root is hypocrisy. The vain one will be told on the Day of Judgement; 'Take what you consider to be the reward of your actions from those you took as your partners with Me. Look to those whom you worshipped and called on, from whom you entertained hopes and whom you feared. And know that you cannot conceal anything inside of you from Allah: you will be deceived by yourself.'
Allah said,
Showing off most frequently occurs in the way people glance at others, speak, eat, drink, arrive somewhere, sit with others, dress, laugh, and in the way they perform prayers, pilgrimage, jihad, recitation of the Qur'an, and all outward acts of devotion.
However, he who is sincere towards Allah, who fears Him in his heart, and who sees himself as lacking even after he has exerted himself with every effort, will find that Allah is contented with him as a result, and he will be among those whom one expects to be free from showing off and hypocrisy, provided he continues to be in that state.
And Quran says:
In the name of Allah, the Beneficent, the Merciful. . Have you considered him who calls the judgment a lie? 1That is the one who treats the orphan with harshness, 2And does not urge (others) to feed the poor. 3So woe to the praying ones, 4Who are unmindful of their prayers, 5Who do (good) to be seen, 6And withhold the necessaries of life. 7
I hear people say inward Shirk is forgivable unlike outward Shirk, but this is false. First the motivation for outward Shirk and reason why it's condemned is because of inward Shirk.
وَقَالَ إِنَّمَا اتَّخَذْتُمْ مِنْ دُونِ اللَّهِ أَوْثَانًا مَوَدَّةَ بَيْنِكُمْ فِي الْحَيَاةِ الدُّنْيَا ۖ ثُمَّ يَوْمَ الْقِيَامَةِ يَكْفُرُ بَعْضُكُمْ بِبَعْضٍ وَيَلْعَنُ بَعْضُكُمْ بَعْضًا وَمَأْوَاكُمُ النَّارُ وَمَا لَكُمْ مِنْ نَاصِرِينَ | He said, ‘You have taken idols [for worship] besides Allah for the sake of [mutual] affection amongst yourselves in the life of the world. Then on the Day of Resurrection you will disown one another and curse one another, and the Fire will be your abode, and you will not have any helpers.’ | Al-Ankaboot : 25
Really, this verse is saying outward Shirk was due to love of affection type amongst themselves, it was a means to unite them.
Furthermore it's impossible to truly believe in God and not do good deeds. It's possible the mind is convinced of Islam, but the heart to be convinced of God would fear God and obey him, otherwise, it's a deception:
وَلَا تَأْكُلُوا مِمَّا لَمْ يُذْكَرِ اسْمُ اللَّهِ عَلَيْهِ وَإِنَّهُ لَفِسْقٌ ۗ وَإِنَّ الشَّيَاطِينَ لَيُوحُونَ إِلَىٰ أَوْلِيَائِهِمْ لِيُجَادِلُوكُمْ ۖ وَإِنْ أَطَعْتُمُوهُمْ إِنَّكُمْ لَمُشْرِكُونَ | Do not eat [anything] of that over which Allah’s Name has not been mentioned, and that is indeed transgression. Indeed the satans inspire their Awliya to dispute with you; and if you obey them then you are polytheists. | Al-An'aam : 121
Furthermore Quran has condemned desiring the life of this world:
مَنْ كَانَ يُرِيدُ الْحَيَاةَ الدُّنْيَا وَزِينَتَهَا نُوَفِّ إِلَيْهِمْ أَعْمَالَهُمْ فِيهَا وَهُمْ فِيهَا لَا يُبْخَسُونَ | As for those who desire the life of this world and its glitter, We will recompense them fully for their works therein, and they shall not be underpaid in it. | Hud : 15
أُولَٰئِكَ الَّذِينَ لَيْسَ لَهُمْ فِي الْآخِرَةِ إِلَّا النَّارُ ۖ وَحَبِطَ مَا صَنَعُوا فِيهَا وَبَاطِلٌ مَا كَانُوا يَعْمَلُونَ | They are the ones for whom there shall be nothing in the Hereafter but Fire: what they had accomplished in the world has failed, and vain/false what they use to do. | Hud : 16
Furthermore Quran has described that it's only those who worship Satan with God that Satan has control over:
فَإِذَا قَرَأْتَ الْقُرْآنَ فَاسْتَعِذْ بِاللَّهِ مِنَ الشَّيْطَانِ الرَّجِيمِ | When you recite the Quran, seek the protection of Allah against the outcast Satan. | An-Nahl : 98
إِنَّهُ لَيْسَ لَهُ سُلْطَانٌ عَلَى الَّذِينَ آمَنُوا وَعَلَىٰ رَبِّهِمْ يَتَوَكَّلُونَ | Indeed he does not have any authority over those who have faith and put their trust in their Lord. | An-Nahl : 99
إِنَّمَا سُلْطَانُهُ عَلَى الَّذِينَ يَتَوَلَّوْنَهُ وَالَّذِينَ هُمْ بِهِ مُشْرِكُونَ | His authority is only over those who give mastery to him and those who make him a partner [of Allah]. | An-Nahl : 100
That means if we believe in God and rely on him, Satan has no authority over us and we will defeat his attempts of controlling us.
Furthermore Quran shows outward belief is not good enough, so inward Shirk is not forgivable:
يَوْمَ تَرَى الْمُؤْمِنِينَ وَالْمُؤْمِنَاتِ يَسْعَىٰ نُورُهُمْ بَيْنَ أَيْدِيهِمْ وَبِأَيْمَانِهِمْ بُشْرَاكُمُ الْيَوْمَ جَنَّاتٌ تَجْرِي مِنْ تَحْتِهَا الْأَنْهَارُ خَالِدِينَ فِيهَا ۚ ذَٰلِكَ هُوَ الْفَوْزُ الْعَظِيمُ | The day you will see the faithful, men and women, with their light moving swiftly in front of them and on their right, [and they are greeted with the words:] ‘There is good news for you today! Gardens with streams running in them, to remain in them [forever]. That is the great success.’ | Al-Hadid : 12
يُنَادُونَهُمْ أَلَمْ نَكُنْ مَعَكُمْ ۖ قَالُوا بَلَىٰ وَلَٰكِنَّكُمْ فَتَنْتُمْ أَنْفُسَكُمْ وَتَرَبَّصْتُمْ وَارْتَبْتُمْ وَغَرَّتْكُمُ الْأَمَانِيُّ حَتَّىٰ جَاءَ أَمْرُ اللَّهِ وَغَرَّكُمْ بِاللَّهِ الْغَرُورُ | They will call out to them, ‘Did we not use to be with you?’ They will say, ‘Yes! But you cast yourselves into perdition. You awaited and were skeptical, and [false] hopes deceived you until the edict of Allah came, and the Deceiver deceived you concerning Allah. | Al-Hadid : 14
فَالْيَوْمَ لَا يُؤْخَذُ مِنْكُمْ فِدْيَةٌ وَلَا مِنَ الَّذِينَ كَفَرُوا ۚ مَأْوَاكُمُ النَّارُ ۖ هِيَ مَوْلَاكُمْ ۖ وَبِئْسَ الْمَصِيرُ | So today no ransom shall be taken from you or the faithless. The Fire will be your abode: it is your [ultimate] refuge and an evil destination.’ | Al-Hadid : 15
This also verified in words of Imam Jaffar (a) in Misbahal Shariah:
Do not show off your actions to someone who neither gives life nor causes death, and who cannot take away from you your burdens. Showing off is a tree whose only fruit is hidden association of other gods with Allah, and its root is hypocrisy. The vain one will be told on the Day of Judgement; 'Take what you consider to be the reward of your actions from those you took as your partners with Me. Look to those whom you worshipped and called on, from whom you entertained hopes and whom you feared. And know that you cannot conceal anything inside of you from Allah: you will be deceived by yourself.'
Allah said,
They desire to deceive Allah and those who believe, and they deceive only themselves and they do not perceive. (2:9)
Showing off most frequently occurs in the way people glance at others, speak, eat, drink, arrive somewhere, sit with others, dress, laugh, and in the way they perform prayers, pilgrimage, jihad, recitation of the Qur'an, and all outward acts of devotion.
However, he who is sincere towards Allah, who fears Him in his heart, and who sees himself as lacking even after he has exerted himself with every effort, will find that Allah is contented with him as a result, and he will be among those whom one expects to be free from showing off and hypocrisy, provided he continues to be in that state.
And Quran says:
In the name of Allah, the Beneficent, the Merciful. . Have you considered him who calls the judgment a lie? 1That is the one who treats the orphan with harshness, 2And does not urge (others) to feed the poor. 3So woe to the praying ones, 4Who are unmindful of their prayers, 5Who do (good) to be seen, 6And withhold the necessaries of life. 7