What would you say to a Muslim who rejects the caliphate/Islamic state is part of Islam?

The concept of the caliphate, or Islamic state, is rooted in the Qur'an and the teachings of the Prophet Muhammad. The Qur'an describes the believers as "a just nation" (Qur'an 2:143) and "a nation of justice" (Qur'an 5:3), and it emphasizes the importance of justice and fairness in society. The Prophet (saw) established a just and fair system of governance in Medina, the Khilafah (caliphate), and he was known for his fair and just leadership. He worked to promote peace, justice, and equality in society, and he was a model of good governance for Muslims to follow. After the death of the Prophet Muhammad, the companions (sahaba) of the Prophet continued with the same system of caliphate governance, which continued to be based on the principles of Islam. The caliphs were responsible for the administration of justice and the protection of the rights of all members of society, regardless of their religion or ethnicity. The caliphs were also responsible for the protection of the Muslim community and the expansion of the Islamic state through military campaigns. However, these campaigns were not motivated by a desire for conquest or domination, but rather they were undertaken in defense of the Muslim community and to spread the message of Islam to other regions. Throughout Islamic history, there have been many examples of just and fair governance under the caliphate system. The caliphs were known for their wisdom, fairness, and justice, and they worked to promote the well-being of all members of their communities. Evidences "O you who have believed, be persistently standing firm in justice, witnesses for Allah, even if it be against yourselves or parents and relatives" (Qur'an 4:135). "O you who have believed, be persistently standing firm in justice, witnesses for Allah, even if it be against yourselves or parents and relatives. Whether one is rich or poor, Allah is more worthy of both. So follow not [personal] inclination, lest you not be just. And if you distort [your testimony] or refuse [to give it], then indeed Allah is ever, with what you do, Acquainted" (Qur'an 4:135). "And do not let the hatred of a people for having obstructed you from the sacred mosque lead you to be aggressive. And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty" (Qur'an 5:2). "And do not let the hatred of a people for having obstructed you from the sacred mosque lead you to transgress. And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty" (Qur'an 5:2). "And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty" (Qur'an 5:2). "And fear Allah and know that Allah is with those who fear Him" (Qur'an 9:120). The Prophet (saw) said, "The best of leaders are those whom the people love and who love the people, who are kind and merciful to them" (Sahih Bukhari). The Prophet (saw) said, "The best of rulers are those whom the people love and who love the people, who are kind and merciful to them. And the worst of rulers are those whom the people hate and who hate the people, who are cruel and hard-hearted towards them. And the best of actions is that which is done with sincerity and the worst of actions is that which is done with insincerity. And the best of guidance is the guidance of Muhammad, peace and blessings be upon him. And the worst of affairs are those which are newly invented, for every newly invented affair is an innovation, and every innovation is a going astray, and every going astray is in the Fire. And the best of speech is that which is straightforward and the worst of speech is that which is convoluted" (Sahih Bukhari). Conclusion The caliphate, or Islamic state, is an important concept in Islam and is rooted in the Qur'an and the teachings of the Prophet (saw). The caliphs were responsible for the administration of justice and the protection of the rights of all members of society, and they worked to promote peace, justice, and equality. It is important for Muslims to understand the importance and significance of the caliphate and to seek knowledge and understanding of the Qur'an and the teachings of the Prophet Muhammad in order to correctly understand and apply the principles of Islamic governance.