As individual every human is 'Khaleefah of Allah'

All human beings, as individual are the 'Khaleefah of Allah' (representatives of Allah) on earth. This is the purport of the following verses:

Wa huwal lazi ja'alakum khala_'ifal ardi wa rafa'a ba'dakum fauqa ba'din darajaa_til liyabluwakum fi maa_ aa_taa_kum

He it is who has made you His Khaleefah of the earth and has exalted some of you in rank above others, that He may try you by (the test of) that which He has given you. [ 6:165]

wa yajalukum hulafa_ al ard a ila_hum ma'al la_h qalilam ma_ tazak karu_n

And He has made you Khaleefah of the earth. Is there any god beside Allah? Little do they reflect! [ 27:62]

Huwal lazi ja_alakum khala_ ifa fil ard faman kafara fa'alaihi kufruh wa la_ yazidul ka_firina kufruhum inda rab bihim il la_ maqta_ wa la_ yazidul ka_firina kufruhum il la_ hasa_ra_

He it is who has made you Khaleefah in the earth; so he who disbelieves, his disbelief is on his own head. Their disbelief increases for the disbelievers, in their Lord's sight, naught save abhorrence. Their disbelief increases for the disbelievers naught save loss. [ 35:39]

These verses show that all human beings are khaleefah of Allah though many of them do not act like khaleefah and in this way commit sins.

About The First Khaleefah Aadam alayhis salaam

Wa iz qa_la rabbuka lil mala_'ikati inni ja_'ilun fil ardi khalifah(tan)

And when your Lord said unto the angels that, "Surely, we are going to place our representative (Khaleefah) on earth". [2:30]

Liabilities and Duties of Khaleefah

Khaleefah means successor of Allah, the one implementing the system set by Allah for the human beings.

fa imma_ ya'tiyannakum minni hudan fa man tabi'a huda_ya fa la_ khaufun 'alaihim wa la_ hum yahzanu_n(a).

But if as is sure there comes to you guidance from Me" whosoever follows My guidance on them shall be no fear nor shall they grieve. [2:38]

This verse of Qur'aan indicates that Khaleefah, as individual, is bound & responsible to obey the divine guidance all over his life and to remain on the righteous path. He, who disobeys the divine guidance, goes false and lives arbitrary life, falls from the representation of Allah .and joins the satanic party (Hizb-ush-Shaiytaan)

The Arrangement to provide the Divine Guidance

To keep the humans on righteous path and to provide them the divine guidance, Allah chooses thousands of Prophets all over the world. The names of some famous prophets are given in the Holy Qur'aan.

Four books were revealed by Allah on four Prophets. Tauraat was revealed on Prophet Moosa (Moses) alayhis salaam, Zaboor on Prophet Dawood (David) alayhis salaam, Injeel on Prophet Eisaa (Jesus) alayhis salaam and the Qur'aan on Prophet Muhammad sallallahu alayhi wasallam.

Why only Four Books and Thousands of Prophets?

In a few words the philosophy of four Books & thousands of prophets seems to be that the righteous persons acting upon the divine guidance are much more imprtant than a lot of Books. It shows the necessity and importance of righteous preachers to the people.