Ibn Bazz: clarify the ruling on and the merits of observing Da`wah (call to Islam) to Allah (Exalted be He)?

Would you please clarify the ruling on and the merits of observing Da`wah (call to Islam) to Allah (Exalted be He)? 

A 1: The ruling on this is from the evidence found in the Qur'an and Sunnah (whatever reported from the Prophet), which indicate that it is obligatory to observe Da`wah to Allah (Glorified and Exalted be He) since it is one of the Fara'id [pl. of Faridah; (obligatory act)]. There are many proofs for this. For example, Allah (Glorified be He) says, Let there arise out of you a group of people inviting to all that is good (Islâm), enjoining Al­Ma‘rûf (i.e. Islâmic Monotheism and all that Islâm orders one to do) and forbidding Al­Munkar (polytheism and disbelief and all that Islâm has صلى االلهforbidden). And it is they who are the successful. Allah (Exalted be He) also says: Invite (mankind, O Muhammad 

to the Way of your Lord (i.e. Islâm) with wisdom (i.e. with the Divine Revelation and the Qur’ân) and fair preaching, and )عليـه و سـلم argue with them in a way that is better. and: and invite (men) to (believe in) your Lord and be not of Al­Mushrikûn (those who associate partners with Allâh, e.g. polytheists, pagans, idolaters, and those who disbelieve in the Oneness of Allâh and deny the Prophethood of Messenger Muhammad صلى االله عليه وسلم). and: Say (O Muhammad صلى االله عليه و سلم): "This is my way; I invite unto Allâh (i.e. to the Oneness of Allâh Islâmic Monotheism) with sure knowledge, I and whosoever follows me (also must inviteotherstoAllâhi.e.totheOnenessofAllâh­IslâmicMonotheismwithsureknowledge). Allah(GlorifiedbeHe)clearly declares that the followers of the Messenger (peace be upon him) are those who call to Allah (Exalted be He). They are the people of wisdom. Accordingly, as it is known, we must follow him and adopt his path )صلى االله عليه وسلمpeace be upon him) as Allah (Exalted be He) says: Indeed in the Messenger of Allâh (Muhammad( you have a good example to follow for him who hopes for (the Meeting with) Allâh and the Last Day, and remembers Allâh much. 

( Part No : 5, Page No: 256) 

However, scholars state that Da`wah to Allah (Glorified and Exalted be He) is a collective obligation in the regions where the Du`ah (callers to Islam) exist, for every region and territory is in need of Da`wah. Being a collective obligation, when it is observed by a sufficient number of people, the others are exempt from blame. Thus, it becomes a confirmed Sunnah and a pious honorable act for those who undertake it. 

However, if Da`wah is completely neglected in a specific area, all the inhabitants are considered sinful. It will become obligatory for every person to observe it according to their ability and capacity. Generally, there must be a group that performs the obligation of Da`wah to Allah (Glorified and Exalted be He), covey Allah's Message, and clarify His Call by all possible means to all people. The Messenger (peace be upon him) sent Du`ah and messages to people, kings, and presidents calling them to Allah (Glorified and Exalted be He).