Not everyone is fit for daʿwah, and not every zealous person is fit for daʿwah, enthusiasm coupled with ignorance is harmful and does not benefit.

Having zeal for the daʿwah is good. A person may have an ambition for Daʿwah and to do good, but it is not permissible for him to enter into the field of daʿwah without having studied, and knowing how to call to Allāh (ʿazza wa jal) and knowing the ways of going about daʿwah. He must have knowledge of that which he wants to call to.

قُلْ هَٰذِهِ سَبِيلِي أَدْعُو إِلَى اللَّهِ ۚ عَلَىٰ بَصِيرَةٍ
“Say (O Muhammad): This is my way; I invite to the way of Allāh with insight”
[Surah Yūsuf, 12:108]

Meaning, (I invite to the way of Allāh) with knowledge. The ignorant one is not fit for daʿwah, (the one involved in daʿwah) must have knowledge, sincerity, patience, forbearance and wisdom. He must also know the path and ways of daʿwah from which the Messenger ﷺ came with.

As for merely having zeal and love for the daʿwah and entering the field of daʿwah with this creates more harm than benefit. This person may fall into problems and cause people to fall into problems. So the likes of this person should suffice with his ambition for good and he will be rewarded for that in shāʾAllāh, but if he wants to enter the field of daʿwah, he should study first. Not everyone is fit for daʿwah, and not every zealous person is fit for daʿwah, enthusiasm coupled with ignorance is harmful and does not benefit.

Source: al-Ajwibah al-Mufīdah ʿan Asiʾlah al-Manāhij al-Jadīdah pg. 143-144.
Translated by: Munīb al-Ṣumālī