The knowledge required by the caller to Allah

Q: What is the knowledge required by the one who calls to Allah, enjoins good, and forbids evil?

A: It is obligatory for the one who calls to Allah, enjoins good, and forbids evil to possess knowledge; because of His saying, the Exalted: [Yusuf: 108]. And knowledge is what Allah stated in His Noble Book, or what the Messenger (peace and blessings be upon him) stated in his authentic Sunnah. This is by each of them paying attention to the Noble Qur'an and the pure Sunnah; so that he knows what Allah has commanded and what Allah has forbidden, and knows the way of the Messenger (peace and blessings be upon him) in his calling to Allah and his forbidding of evil, and the way of his Companions (may Allah be pleased with them). He should reflect on this by reviewing the books of hadith, along with paying attention to the Noble Qur'an, and reviewing the statements of the scholars in this chapter, for they have expanded on the discussion of this and explained what is obligatory. And the one who takes up this matter must pay attention to it until he is on clear understanding of the Book of Allah and the Sunnah of His Messenger (peace and blessings be upon him), so that he places things in their proper places; placing the call to good in its place, and the enjoining of good in its place with clear understanding and knowledge; so that he does not fall into forbidding evil in a manner that is more evil than it, and so that he does not fall into enjoining good in a manner that necessitates the occurrence of an evil more dangerous than leaving that good which he is calling to.
And the point is that he must have knowledge so that he places things in their proper places.