What is the scientific methodology in calling people to Allah?

The questioner : What is the scientific methodology in calling people to Allah, or the books with which one can begin in these groups?

The Shaykh : In these groups?

The questioner : Yes, the ones that have multiplied now; perhaps their multiplication is a multiplication of contradiction rather than diversity?

The Shaykh : By Allah, the answer to a question like this goes back to the method of learning knowledge. Whoever is a scholar is the one who can graduate with any group. For example, if a person is afflicted with an atheist, how does he graduate with him? How does he deal with him? How does he debate him? We go down from this atheist to a Jew, to a Christian, to a misguided Muslim, an Ibadi, a Maturidi, an Ash'ari, and so on. How? I say the answer to this requires knowledge. Whoever is a scholar, and knowledge has levels, yes, he may be able to debate a Muslim who has deviated from the Shari'ah, but he cannot debate a heretic, for example, or a Jew or a Christian, because he does not have knowledge of what these people have in their books that they respect and sanctify, and their prophets, some of whom they believe in and some of whom they declare disbelievers, and so on. So it is not easy, and with one word, to give you a methodology for how to call these people, whose separation and difference may be a difference of contradiction or a difference of diversity. This requires scholars, and this is our problem: the land is barren regarding the scarcity of scholars. Our advice is that students of knowledge should work to become scholars. If they do not become scholars, they will be able to take charge of guiding everyone who contacts them, each according to his belief, his sincerity, his deviation, and so on. So the point is that a brief and concise answer to a question like this is not possible.