Allaah Ta`aalaa says in the Qur'aan:
قل هذه سبيلي أدعو إلى الله على بصيرة أنا ومن اتبعني
"Say (O Ambiyaa): This is my path. I call towards Allaah with Baseerah; I and those who follow me..."
The `Ulamaa have explained "Baseerah" in this Aayah as meaning `Ilm (Knowledge of Deen).
So, one of the main requirements of Da`wah is `Ilm. A person has to have `Ilm in order to give Da`wah. Otherwise, instead of guiding people, he might end up misguiding people instead, and thus ruin his own Aakhirah.
These days, there are so many people who create YouTube channels, speaking on Islaam when some of them can't even read the Kalimah. If a person is not a doctor, he will not open up a surgery. If he does, he'll get arrested. Why? Because the people take life seriously. Deen is infinitely more important. If he is not a "doctor" in Deen, then he should not open a "surgery".
There is a saying, in Farsi:
Neem Hakeem Khatre Jaan, Neem Aleem Khatre Imaan.
"Half a doctor is a danger to your life, but half an `Aalim is a danger to your Imaan."
First gain sufficient `Ilm, then give Da`wah.
والسلام