The knowledge that must be possessed by the caller to Allah

Question:
Is knowledge and understanding of the religion a condition that must be met by one who calls to Allah? What is your opinion of those who make knowledge one of the programs of their da'wah, yet they insult and belittle the scholars and students of knowledge, explicitly and by implication, saying: "They are sitting reading books, while the ummah (the Muslim community) is burning and dying upon other than the religion?"

Answer:
It is not a condition of calling to Allah that a person possess all knowledge and strive to know every matter. No, he calls to Allah according to his knowledge. If he knows one issue, he calls to it; if he knows two issues, he calls to them; if he knows three, he calls to them, and so on. He continues to learn and deepen his understanding of the religion, and he takes care of knowledge, until he gains insight.
But if he knows something of the religion of Allah, of the Shari'ah (Islamic sacred law), such as prayer, and he knows that prayer is obligatory (fard), that it is the pillar of Islam, that it is obligatory for men to perform it in congregation, and that ritual purity is a condition for it and is necessary, he calls to this which he knows. He knows that zina (unlawful sexual intercourse) is forbidden (haram), he knows that khamr (intoxicants) is forbidden. He does not need to learn about other matters in order to enjoin this and forbid that. No, these are apparent and well-known matters. Even if a person is in primary school, or middle school, or high school, it is a known matter that a believer adheres to and calls to, and it is known to be forbidden, so he warns against it and forbids people from it.
And whatever is ambiguous to him, he does not rush in it. Whatever he has no knowledge of, whatever is ambiguous to him, he does not rush; he does not speak about it. Rather, he says: "I do not know," until he learns, until he gains insight. But the matters he has learned and known, such as knowing prayer, that it is truth, that it is religion, and that it is the pillar of Islam, he calls to it and rebukes those who abandon it. He knows zakah (the obligatory alms), that it is a right upon wealth, so he calls to it. He knows fasting in Ramadan, that it is truth, and that it is one of the pillars of Islam, so he fasts, he commands people to fast, and he rebukes those who abandon fasting.
He knows dutifulness to parents, that it is a right, and that undutifulness to parents is forbidden (haram) and a major sin, so he rebukes one who is undutiful to his parents and commands him to be dutiful. He knows that false testimony is forbidden (haram), so he rebukes one who gives false testimony and lies. He knows that zina (unlawful sexual intercourse) is forbidden (haram), so he rebukes one who engages in zina and its means. He knows that khamr (intoxicants) is forbidden (haram), so he rebukes one who drinks khamr. This is how the believer proceeds, meaning he acts upon what he knows, and what he does not know, he holds back until he learns.