From Muhammad, Messenger of Allah, to Jaifar and 'Abd, sons of al-Julanda, and may peace be upon those who follow Allah's guidance. To proceed, I invite you both to Islam; accept Islam and you will attain salvation, for I am Allah's Messenger to all mankind so that I may warn those who are alive and establish (Allah's) word over the unbelievers. If you declare your Islam I will appoint you both as governors [of your lands], but if you refuse then (know that) your dominion is only fleeting, and my horsemen will dismount in your courtyard, and my Prophethood will prevail over your dominion.
“Al-Qurtubi, as well as other scholars, said that this Āyah (2:30) proves the obligation of appointing a Khalīfah to pass judgements on matters of dispute between people, to aid the oppressed against the oppressor, to implement the Islamic penal code and to forbid evil. There are many tasks that can only be fulfilled by appointing the Imam, and what is necessary in performing an obligation, is an obligation itself.” [Tafsir Ibn Kathir, Vol. 1 p. 185]
"and that would be part of the dīn of Allah which is obliged for him, just as every responsible person knows from the dīn of Allah what is obliged for him regarding the five prayers, fasting Ramadan, ḥajj and the like"
The following is related by Al-Wahidi in his Asbab al-Nuzul [The Circumstances of Revelation] regarding Surah 38 verses 5 to 12 “When ‘Umar ibn al-Khattab embraced Islam, the Muslims were overjoyed while the Quraysh was devastated. Al-Walid ibn al-Mughirah said to the nobles and chiefs of Quraysh: ‘Go to Abu Talib and say to him: … Continue reading The Political Significance of the Kalimah
When your Lord said to the angels, ‘I am putting a khalif on the earth,’ they said, ‘Why put on it one who will cause great corruption on it and shed blood when we glorify You with praise and proclaim Your purity?’ He said, ‘I know what you do not know.’ [2:30] ‘I am … Continue reading The Caliphate in Tafsir al-Qurtubi