What is the correct methodology in Salafi da'wah, especially in this time when trials have multiplied and knowledge has diminished?

The questioner : May Allah reward you with good, O honorable father. We ask you to clarify for us what the correct methodology is in Salafi da'wah, especially in this time when trials have multiplied and knowledge has diminished. We also ask for clarification on the difference between organization, arrangement, and guidance. May Allah reward you with good.

The Shaykh : As for da'wah, it cannot be established except by those who possess knowledge and uphold justice. As for what has become widespread in this time, where many people who have been given only a negligible share of knowledge call themselves da'wah workers for Allah, this is, in my opinion—and you may find this surprising, but I bear the responsibility for what I say—one of the innovations of the modern era. It is an innovation of the modern era that it is now widespread among people that there are thousands of da'wah workers who have no knowledge of the Book, nor of the Sunnah, nor of the reports of the Salaf, nor even of the established traditional schools of jurisprudence today. They only know some simple rulings, and perhaps some verses and some hadiths that the least knowledgeable person could recite. Then they appoint themselves as da'wah workers. When asked about a certain issue, they are perplexed and unable to answer, or they may answer out of complete ignorance. This is one of the plagues of the modern era. The matter does not stop with these young upstarts; rather, we may find great men who have not been given that ample share of knowledge, yet they have become famous as da'wah workers for what?!
For Islam, while they fight Islam by fighting the Sunnah, without which a Muslim cannot understand the Book of Allah except through the Messenger of Allah (peace and blessings be upon him). How can one be a da'wah worker for Islam if he is ignorant of the Sunnah in terms of knowledge, and then fights it in some of its aspects, at least in terms of creed? This person is not fit to be a da'wah worker for Islam, except in the manner I mentioned to you earlier. I hope you will pay attention to my wording so that my words are not misquoted: except in the manner—what I mean as an example—of what I mentioned earlier regarding the Qadiyyan. They are the most active Islamic sect in da'wah to Islam, but this da'wah is not to Islam, but to their own Islam, which has taken them out of the circle of the inherited Islam, following the Khalaf after the Salaf. Similarly, there are today some da'wah workers who have not been given an ample share of knowledge of the Sunnah, by the light of which the Noble Qur'an can be interpreted correctly. So what does one say about such people? Rather, what do we say about the modern upstarts, where hardly one of them graduates from high school, let alone obtain a higher degree, even a doctorate, even in Shari'ah? They have not yet learned much of the rulings of the Shari'ah. What do we say about these people who have appointed themselves for da'wah to Islam, when he (peace and blessings be upon him) said, as in Sahih al-Bukhari and Sahih Muslim from the hadith of Abdullah ibn Amr ibn al-As, that the Messenger of Allah (peace and blessings be upon him) said: I know some muftis in some Arab Islamic countries, not the non-Arab countries, who were asked about foreign female servants who are brought to some Islamic countries as maids. Is it permissible for these non-Muslim female servants to see the Muslim lady of the house uncovered, or must she veil herself before them as she veils herself before foreign men, as is explicit in the Qur'an in the saying of Allah, Blessed and Exalted is He: until He said at the end of the verse: or their Muslim women. These are the ones before whom a Muslim woman is permitted to appear with her head, arms, feet, and the lower part of her calves uncovered. As for anything else, she lives uncovered, exposing her chest and her upper arms, because she takes her freedom in her own home, but she has a non-Muslim, a non-Muslim maid. Do you know what he answered?!
He answered that it is permissible by analogy to the slave women, i.e., the female slaves who were taken by a lawful means, so that she would be their mistress. And we know from the Sunnah that the male slave of a woman is permitted to see of her what is permitted for her mahram to see of her. It was narrated in Sunan Abu Dawud: So, a fortiori, if it is a woman. He analogized this non-Muslim maid, who is not a slave owned by her, to the owned slave. Does not the saying of him (peace and blessings be upon him) mentioned earlier apply to such a person: This man holds a high position. So what do we say about the modern generation that appoints itself for da'wah, claiming it is to Islam, while they know only a little of Islam?!