The Obligation of the Call and the Duty of the Caller
Concise explanation given by the shaykh in regards to questions like: What is the requirement of being a dāʿī? Is daʿwah for men as well as women? What is the most fundamental duty of the caller? And a much-needed clarification as to why we don’t differentiate between the Scholar and the caller.
As for the saying of some of the people that it is permissible to become duʿāʾʾʾt (callers) without having knowledge, then if they mean a dāʿī without a huge amount of knowledge, able to give fatāwá (religious verdicts), explain and deduce issues from their proofs – then it is possible to accept this saying.
[Q.1]: Is daʿwah (calling) to Allāh obligatory upon every Muslim man or woman, or is it to be left for the Scholars and the students of knowledge only? Is it permissible for the lay person to call to Allāh?
[A.1]: When a person has knowledge and insight into that which he is calling to, then there is no difference between the one who has a great amount of knowledge, or a student of knowledge who has recently started in pursuit of knowledge, or a lay person – as long as he has certain knowledge of the issue at hand. The Prophet (ṣallallāhu ʿalayhi wa-sallam) said: “Convey from me, even if it is one āyah.”  So it is not a condition upon the dāʿī (caller) to attain a great amount of knowledge, but the condition is that one must have knowledge of what one is calling to. If this calling is established upon ignorance and passion, then it is not permissible.
Thus, we see that some of the brothers who call to Allāh, they do not have except a little knowledge. We see them, due to their strong emotions, prohibiting that which Allāh has not prohibited, whilst making obligatory that which Allāh has not made obligatory upon his worshippers. This is a very dangerous matter, since permitting what Allāh has made ḥarām (unlawful) is like prohibiting what Allāh has made ḥalāl (lawful). So when they begin prohibiting people from making a certain matter ḥalāl, then others will rebuke them for making it ḥarām. Allāh the Most High says: “And do not say, concerning that which your tongues falsely put forward, ‘This is lawful and this is prohibited,’ so as to invent lies against Allāh. Indeed those who invent lies against Allāh will never prosper.” [Sūrah al-Naḥl, 16:116-117]
As for the lay person, then he must not call to Allāh if he does not have knowledge. Rather, it is essential to have knowledge, in accordance to the statement of Allāh the Most High: “Say: This is my path, I call unto Allāh upon sure knowledge.” [Sūrah Yūsuf, 12:108]
So it is a must to call to Allāh upon knowledge. However, if a matter is clearly known to be evil or good, then one can command it – if it is good, or prohibit it – if it is evil.
So the callers to Allāh must start with knowledge. Whosoever calls to Allāh without knowledge, then such a
person will cause greater harm than good – as is evident. So it is obligatory upon a person to first acquire knowledge, then to give daʿwah. As for the clear evils, and that which is clearly good, then the good is enjoined and the evil prohibited. 
[Q.2]: What is the difference between a Scholar and a dāʿī?
[A.2]: The difference between the Scholar and the dāʿī is clear. The dāʿī is the one who strives to convey the message of the Sharīʿah to the servants of Allāh. He calls them, sometimes by means of targhīb and tarḥīb (persuasion and deterring).
The Scholar is the one to whom Allāh has given knowledge and who may, or may not be a dāʿī. However, if the Scholar is not a dāʿī, then he is extremely deficient in his knowledge, and not a complete inheritor of the Messenger of Allāh ṣallallāhu ʿalayhi wa-sallam). This is because the Prophets (ʿalayhimus-ṣalātu was-salām) did not bequeath the dirham nor the dīnār as inheritance, but they bequeathed knowledge, as the Prophet ṣallallāhu ʿalayhi wa-sallam) said: “Indeed the Scholars are the inheritors of the Prophets, and indeed the Prophets do not leave behind them the dīnār nor the dirham as inheritance. They leave behind only knowledge as inheritance. So whosoever acquires it acquires a huge fortune.”  Consequently, whoever acquires knowledge and calls to Allāh, then such a person has truly inherited from the inheritance of the Prophets – in proportion to what he establishes and implements from their prescribed laws.
As for the saying of some of the people that is is permissible to become duʿāʾʾʾt (callers) without knowledge, then if they mean a dāʿī without a huge amount of knowledge, able to give fatāwá (religious verdicts), explain and deduce issues from their proofs – then it is possible to accept this saying. However, if they mean a dāʿī not having knowledge what to give daʿwah to, nor having knowledge what to give daʿwah with, then there is no doubt that this cannot be. And I warn people from calling to the truth in this manner, since the harm caused is greater than the goodness achieved, as can be seen! 
 Related by al-Bukhārī (no. 3461) from ʿAbdullāh Ibn ’Amr (raḍī Allāhu ʿʿʿanhu).
 Taken from al-Sahwat al-Islāmiyyah (p. 75-76) of Shaykh Ibn al-ʿUthaymīn, as compiled by ʿAlī Abū Lawz.
 Ḥasan: Related by Abū Dāwūd (no. 3461) and Ibn Mājah (no. 223) from Abū al-Dardāʾ (raḍī Allāhu ʿʿʿanhu). It was authenticated by Shaykh al-Albānī in his checking upon Sharḥ al-Sunnah(1/276).
 Taken from al-Sahwat al-Islāmiyyah (p. 76-77)