All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
Da‘wah is mandatory for every Muslim who has reached an age by which he is held accountable for his deeds. Every such Muslim is required to practice Da'wah in accordance with his ability and knowledge.
The Prophet, sallallaahu ‘alayhi wa sallam, ordered us to convey part of what he, sallallaahu ‘alayhi wa sallam, brought forth, even if that was just one verse from the Quran. [Al-Bukhari]
However, a person who invites others to Allaah The Almighty has to do this on the basis of knowledge and insight. Allaah Says (what means): {Say, "This is my way; I invite to Allaah with insight, I and those who follow me. And exalted is Allaah; and I am not of those who associate others with Him."}[Quran 12:108]
This does not mean that a person should not practice Da‘wah until he becomes a scholar, but rather he is required to be knowledgeable about the issue he addresses people with and its relevance to the receiving party, and what the most effective approach to that person in particular would be.
Allaah Knows best.