This is one of the aayaat that our righ teous predecessors extract the rules/principles/basics of Da'wah from. The Arabic term is Usool ad-Da`wah and is used interchangeably with the word Minhaaj.
The instruction that follows is the Sunnah of Da`wah, and it is very important that it be adhered to. It is as follows:
There is a science of the Arabic language in which a part of a phrase can be used when it is actually referring to the whole phrase. This science is being applied when the aayah states to Allaah because it is referring to the Kalimah (Laa ilaaha illaallaah). The reverse of this is also a science in which an entire phrase is used when it is actually referring to part of a phrase, e.g. <<They thrust their fingers into their ears... >>(2:19) The word fingers is used but it is actually referring to the fingertips (of possibly only two fingers yet the Jam` case of three or more is used).
So it is here that Allaah tells us to invite the people to Tawheed. Clearly notice that we are not commanded to summon the people to any individual (regardless of how knowledgeable), any organization or masjid, any way of thinking, any project, nationalism, interfaith dialogue, ism or schism, etc. We are only commanded to call the people to the meaning of Laa ilaaha illaallaah.
Baseerah means Daleel and Burhaan (clear proofs and evidences). The word Daleel literally means guide. Often people ask the question "What is your Daleel (evidence/proof from the Quraan and authentic Sunnah)?" So what they are literally asking for is "guidance" because this is what revelation does - it guides us. Thus, this is HOW we invite the people toTawheed: with proofs/evidences from the Ouraan and authentic Sunnah!
Evidence can be produce by two basic ways:
One of our eminent scholars, Ibn al Qayyim al-Jawzeeyah stated, "Knowledge is what Allaah says, what the Prophet says, and what the Companions say."
Therefore, in light of the above, one must, be knowledgable in whatever he is inviting the people to. This is a very important condition of Baseerah because if one does not know what he's talking about he could be inviting people to Kufr and Shirk and Bid`ah and Kabaa'ir and other Muharaamaat. The Prophet said, The seeking of knowledge (of religious matters) is mandatory upon every Muslim (al-Bayhaqee); and Allaah says, <<Everyone must know that there is none worthy of worship except Allaah>>(47:19) and <<invite to Allaah with clear knowledge>>(12:108).
A second condition of Baseerah is that the daa`ee (inviter) should be familiar with whom he is giving da`wah to. This is important because having this knowledge may be benefcial in convincing the invitee(s) to accept Islaam because the daa`ee would know how (or how not) to approach his audience. When the Prophet commissioned Mu`aadh to be the governor of Yamaan, he abreasted him that he was assigning him to an area that was predominately of Jews and Christians (see Bukhaaree vol.9 #469 and Muslim vol. 1 #27). With this information it would be useful for Mu`aadh to know that he would be around people who had some knowledge of the previously-revealed divine scriptures because the approach we use with a Confucianist would not necessarily be the same approach we use for a Sabean or for a Christian, etc. Likewise, it may be better to send our Muslim brother Mustafaa O'Connell to Ireland than it would be to send someone of British origin (because generally people are more comfortable with others who are similar to themselves - and notwithstanding the ongoing conflict between the two nations).
This hadeeth concerning Mu`aadh is also a proof for the first condition of Baseerah because the rest of the hadeeth informs us that the Prophet told Mu`aadh to instruct the people in the basics of Islaam. In order for Mu`aadh to do this he himself would first have to have knowledge of Tawheed, Ittibaa` ar-Rasool, Tahaarah, Salaah, etc. And let us take special note that the first tbing that the Prophet ordered him to do was: invite the people to Laa ilaaha illaallaah.
A third condition of Baseerah is to be respectful, polite, humble, and the like, yet not compromising any Islaamic principles (like shaking hands with the opposite sex or sipping non-virgin cocktails) -while conveying the Da`wah. Allaah instructed Moosaa and Haaroon <<Both of you go to Fir`awn for without a doubt he has transgressed, and speak to him with kind and gentle words>>(20:43,44), and <<If you had been severe and harsh-hearted they would have ran away from you>>(3: 159). Furthermore, we should not insult those things that the disbelievers worship besides Allaah, e.g. in the 70's when I was a member of the Nation of Kufr (the "so called" Nation of Islam) I used to say to my parents "How can we you worship that white, blue-eyed, hippie devil [Jesus]?' Although, both of us was in a state of disbelief when I accosted them in this manner it naturally brought about a defensive response (which will make it harder to convice someone of your point). To ridicule and blaspheme the gods that people worship besides Allaah is in opposition to Allaah's command <<Do not revile those whom they pray to besides Allaah because they will wrongfully revile Allaah>> (6:108).
Also, we don't use rap songs to give Da`wah. Yes, music and instruments existed in the time of the Companions, yet with their knowledge, understanding, wisdom, and practice of Islaam (that will not be superceded by any other generation before their time and after it) did not use music to give Da`wah. In fact they did not listen to music at all.
This third condition of Baseerah means that we do not tell the people the consequences Allaah has planned for anyone who does not live according to His prescriptions and proscriptions. From several aayaat and ahaadeeth we can see that it is the Sunnah of Allaah and the Sunnah of His Messenger to tell the people about dreadful and tormenting punishments for the disobedient.
The Arabic word man is a particle that is general. It is not restricted to any place or time. Whether one is a companion of the Prophet , or is born of Slavic descent, or lives in 17th century Salem, or emerges from the pre-historic Flintstone age, or plays golf on the moon, the whomever, wherever, and whenever does not make any difference - as long as he is following the Prophet he is abiding by the dictates of Allaah. <<Whoever obeys the Messenger has obeyed Allaah>>(4:80).
The Da`wah of Islaam has three aspectsto it: Tawheed(monotheism),Ittibaa` ar-Rasool (following the Messenger: Sunnah), and Tazkeeyah (sanctification of the heart: the result of believing in Tawheed and following the Sunnah).