Kindness and mercy towards the believers and harshness and strength towards the kuffar are evidence of sincerity and correct knowledge. So it is wise to seek knowledge from the people of jihad.

وَٱلَّذِینَ جَـٰهَدُوا۟ فِینَا لَنَهۡدِیَنَّهُمۡ سُبُلَنَاۚ وَإِنَّ ٱللَّهَ لَمَعَ ٱلۡمُحۡسِنِینَ

And those who strive for Us – We will surely guide them to Our ways. And indeed, Allah is with the doers of
good.

26:69

From kindness and mercy towards the believers is to avoid excessive disputing and arguing. Imam Shafi’i, rahimullah, said:

من إِذَالَةِ العلم أن تناظر كلَّ من ناظرك وتُقاوِلَ كلَّ من قَاوَلَك

“Debating everyone who debates you and arguing with everyone who argues with you is degradation of
knowledge.”

Manāqib al-Shāfi’ī lil-Bayhaqī 2/151

And Imam Malik, rahimullah, is reported to have said:

الجدال مع الناس ينزع بركات العلم من قلبه

“Arguing with the people removes the blessing of knowledge from the heart.”

Harshness towards the kuffar and gentleness towards the believers are interconnected. Someone who leaves off fighting the kuffar will become harsh with the believers, and someone who abandons kindness with the believers will become soft against the kuffar.

So if we are affected by excessive argument with the Muslims, one of the cures is to increase focus on fighting and combating the kuffar. If we find ourselves unmotivated to fight the kuffar, one solution is to cultivate mercy, love and compassion for the believers within ourselves. This can be accomplished by seeking to help and support Muslims who are in a vulnerable position, whether it be orphans, prisoners, or the poor.

In attempting to help these Muslims, we will become more aware of their suffering and its causes, and we will be more motivated to act to remove the root cause of the problem. The root cause of the problems we are facing in the world today is our failure to implement the command of Allah, and the spread of injustice, or dhulm, as a result— shirk being the foremost instance of dhulm.

Acts of kindness toward believers create a bond of love in both directions; for the one making du’a for his brother, and the one for whom the du’a is made. For the one giving a gift, and the one receiving it. As this compassion for the Muslims increases, its natural result is increasing enmity towards the ones who harm and attack Islam and the Muslims. So if you have difficulty with motivation to jihad, connect with your brothers and sisters who are facing difficulty.

Connect with them by making du’a for them, by supporting them materially, by offering words of support and kindness, by listening to the hardship they are facing, by informing other Muslims about their situation, and by trying to help improve their situation in any way you can. Then contemplate the causes of their hardship and how to relieve it.

The nature of love is that the stronger it grows, the more you hate whatever harms your beloved. If you claim to love someone, but do not hate injustice to be done to them, this is not a true or sincere love. This points to the wisdom and benefits of following the sunnah. For one, helping your Muslim brothers and sisters is in itself a powerful act of worship.

عَنِ ابْنِ عُمَرَ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ أَحَبُّ النَّاسِ إِلَى اللَّهِ أَنْفَعُهُمْ لِلنَّاسِ وَأَحَبُّ الأَعْمَالِ إِلَى اللَّهِ سُرُورٌ تُدْخِلُهُ عَلَى مُسْلِمٍ أَوْ تَكْشِفُ عَنْهُ كُرْبَةً أَوْ تَقْضِي عَنْهُ دِينًا أَوْ تَطْرُدُ عَنْهُ جُوعًا وَلَأَنْ أَمْشِيَ مَعَ أَخِيهِ فِي حَاجَةٍ أَحَبُّ إِلَيَّ مِنْ أَنْ أَعْتَكِفَ فِي هَذَا الْمَسْجِدِ يَعْنِي مَسْجِدَ الْمَدِينَةِ شَهْرًا وَمَنْ كَفَّ غَضَبَهُ سَتَرَ اللَّهُ عَوْرَتَهُ وَمَنْ كَظَمَ غَيْظَهُ وَلَوْ شَاءَ أَنْ يُمْضِيَهُ أَمْضَاهُ مَلأَ اللَّهُ عَزَّ وَجَلَّ قَلْبَهُ أَمْنًا يَوْمَ الْقِيَامَةِ وَمَنْ مَشَى مَعَ أَخِيهِ فِي حَاجَةٍ حَتَّى أَثْبَتَهَا لَهُ أَثْبَتَ اللَّهُ عَزَّ وَجَلَّ قَدَمَهُ عَلَى الصِّرَاطِ يَوْمَ تَزِلُّ فِيهِ الأَقْدَامُ

Ibn Umar reported: The Prophet ﷺ said, “The most beloved people to Allah are those who are most beneficial to people. The most beloved deed to Allah is to make a Muslim happy, or to remove one of his troubles, or to forgive his debt, or to feed his hunger. That I walk with a brother regarding a need is more beloved to me than that I seclude myself in this mosque in Medina for a month. Whoever swallows his anger, then Allah will conceal his faults. Whoever suppresses his rage, even though he could fulfill his anger if he wished, then Allah will secure his heart on the Day of Resurrection. Whoever walks with his brother regarding a need until he secures it for him, then Allah Almighty will make his footing firm across the bridge on the day when the footings are shaken.”

al-Muʻjam al-Awsaṭ 6/139

This support is also beneficial to our worldly lives. If you are facing any difficulties in your own life, helping and supporting your brothers and sisters in need can also help to resolve your problems.

The Prophet ﷺ said:

وَاللَّهُ فِي عَوْنِ الْعَبْدِ مَا كَانَ الْعَبْدُ فِي عَوْنِ أَخِيهِ

“And Allah helps the servant as long as he helps his brother.”

Ṣaḥīḥ Muslim 2699

Contrary to the claims of humanists, this harshness towards the disbelievers and kindness with the believers is actually the most compassionate course of action for all of humanity.

كُنتُمۡ خَیۡرَ أُمَّةٍ أُخۡرِجَتۡ لِلنَّاسِ تَأۡمُرُونَ بِٱلۡمَعۡرُوفِ وَتَنۡهَوۡنَ عَنِ ٱلۡمُنكَرِ وَتُؤۡمِنُونَ بِٱللَّهِۗ وَلَوۡ ءَامَنَ أَهۡلُ ٱلۡكِتَـٰبِ لَكَانَ خَیۡرࣰا لَّهُمۚ مِّنۡهُمُ ٱلۡمُؤۡمِنُونَ وَأَكۡثَرُهُمُ ٱلۡفَـٰسِقُونَ

You are the best nation produced [as an example] for mankind. You enjoin what is right and forbid what is
wrong and believe in Allah. If only the People of the Scripture had believed, it would have been better for
them. Among them are believers, but most of them are defiantly disobedient.

3:110

Even with the degraded state of the ummah today, the Muslims still are at the forefront of opposing the world’s destructive riba-based economic system, preserving the integrity of the family, and opposing idolatry and materialism. A strong and healthy Muslim ummah is the best thing that can happen to humanity, because a strong ummah will act as a beacon of guidance and a proof of Islam, and a force for establishing morality and opposing immorality.