In addition, some Muslims include Jihad and Dawah as part of "aqidah"  Jihad (to struggle) and literally means to endeavor, strive, labor to apply oneself, to concentrate, to work hard, to accomplish. It could be used to refer to those who physically, mentally or economically serve in the way of God. Da‘wah ("invitation") means the proselytizing or preaching of Islam. Da‘wah literally means "issuing a summon" or "making an invitation," being an active participle of a verb meaning variously "to summon" or "to invite." A Muslim who practices da‘wah, either as a religious worker or in a volunteer community effort, is called a dā‘ī (داعي plural du‘āh, gen: du‘āt دعاة). A dā‘ī is thus a person who invites people to understand Islam through dialogue, not unlike the Islamic equivalent of a missionary inviting people to the faith, prayer and manner of Islamic life. Eschatology is literally understood as the last things or ultimate things and in Muslim theology, eschatology refers to the end of this world and what will happen in the next world or hereafter. Eschatology covers the death of human beings, their souls after their bodily death, the total destruction of this world, the resurrection of human souls, the Last Judgment of human deeds by God after the resurrection, and the rewards and punishments for the believers and non-believers respectively. The places for the believers in the hereafter are known as Paradise and for the non-believers as Hell. Muslim theology is the theology and interpretation of creed ("aqidah") that derived from the Qur'an and Hadith. The contents of Muslim theology can be divided into theology proper such as theodicy, eschatology, anthropology, apophatic theology, and comparative religion. In the history of Muslim theology, there have been theological schools among Muslims displaying both similarities and differences with each other in regard to beliefs. "Kalām" is "Islamic scholastic theology" of seeking theological principles through dialectic. In Arabic, the word literally means "speech/words." A scholar of "kalām" is referred to as a "mutakallim" (Muslim theologian; plural "mutakallimūn"). There are many schools of Kalam, the main ones being the Ash'ari and Maturidi schools in Sunni Islam.