Definition of Khilafa and Khalifa
Khalifa is an Arabic word literally meaning "one who replaces someone else who left or died" (English: caliph). In the context of Islam, however, the word acquires a narrower meaning. The Muslim Khalifa is the successor (in a line of successors) to Prophet Muhammad's (saw) position as the political, military, and administrative leader of the Muslims. The prophetic role of Muhammad is strictly not included in this definition, as the Qur'an and Hadith clearly state that Muhammad was the last of the prophets. Khilafa is a related Arabic word which, in the context of Islam, is used to denote the government of the Muslim state, of which the Khalifa is the head. A workable analogy of Khalifa and Khilafa is president and presidency or king and monarchy. The Khilafa is a fard kifaya on the ummah.
The duties and responsibilities of the Khalifa
The Khalifa of the Muslim ummah must strive to:
Safeguard Islam in its original form, and to protect against the introduction of new things (bid'a) into Islam.
Establish justice (including punishments for crimes) among the people.
Ensure the protection of the ummah. People within the boundaries of the Muslim state (regardless of whether they are Muslims or not) should feel secure enough to be productive.
Protect the physical boundaries of the state through the use of arms and other methods.
Defend the rights of Muslims abroad, and to see to it that Islam can spread freely in non-Muslim lands (including the use of force).
Organize jihad against any non-Muslim government which prevents Muslim da'wah from entering its land.
Collect and distribute zakat and the spoils of war according to the Qur'an and Sunnah (and ijtihad, if necessary). This must be done without the use of fear as an incentive (unless a person refuses to pay). Zakat is not to be taken from the best or worst of people's possessions, but rather from the middle.
Pay the salaries of Bayt-ul-Mal employees, i.e., those people whose job is the collection of zakat and other state-levied taxes. Their salaries should be reasonable and be paid on time.
Hire honest people as helpers, aides, governors, etc. The Khalifa must appoint to public office those who are competent and who can give good advice. This especially applies to Bayt-ul-Mal officials.
Be heavily involved personally in the acts of governing. The Khalifa must be actively checking and overseeing the duties of the government, and constantly be guarding against internal corruption.
The prerequisites to becoming the Khalifa
Muslim scholars have determined certain criteria which any possible candidate for the Khalifa must meet to be considered legitimate.
The Khalifa must be Muslim.
He must be a man. This condition is based on the hadith where the Prophet states that a nation would not profit under a woman as its leader.
He must be knowledgeable in Islam, and be able to make independent decisions if necessary.
He must be just, have good morals, and be trustworthy.
He must be physically able (non-handicapped), spiritual, brave, and helpful to protect the ummah against its enemies. His eyes, ears, tongue, and body in general should be in working condition. The point here is to stress an independent, dynamic leader for the sake of the ummah, not to discriminate against the physically handicapped. Today, for example, an artificial limb could be used to offset an otherwise crippling injury.
He must be politically, militarily, and administratively experienced.
He must be from the tribe of Quraish because they used to be the leading tribe, the majority. The Prophet has said, "The Khalifas are Quraishi." However, many Muslim scholars have commented on this prerequisite. Al-Mawardi has written that the Khalifa should be Quraishi based on the saying of Abu Bakr that the Khalifas are Quraishi and their ministers are non-Quraishi. The majority of scholars are of this opinion. Other scholars have arrived at a different conclusion. Abu Bakr Al-Baqlani has said that the leader of the Muslims simply should be from the majority. Muhammad Riya-Ad-Deen and Abu Hanifa wrote that the leader must come from the majority to make it easy to follow him.
How the Khalifa may be chosen
There are three ways in which the Muslim ummah may choose a new Khalifa. However, in all three cases, the people are obligated to give the new Khalifa their bay'a once the process of choosing him is over. People can send representatives to give their bay'a if the population is large. The three ways of choosing the Khalifa are by selection, by nomination, and by force.