Calling people to Allaah is one of the best and noblest of deeds before Allaah, may He be glorified and exalted. How could it be otherwise, when this is the role of the Prophets and Messengers whom Allaah chose from among His creation, and of those who inherited their role, namely the scholars and daa’iyahs? Allaah says (interpretation of the meaning):
“Say (O Muhammad صلى الله عليه وسلم): This is my way; I invite unto Allaah (i.e. to the Oneness of Allaah — Islamic Monotheism) with sure knowledge, I and whosoever follows me (also must invite others to Allaah, i.e. to the Oneness of Allaah — Islamic Monotheism with sure knowledge). And Glorified and Exalted be Allaah (above all that they associate as partners with Him). And I am not of the Mushrikoon (polytheists, pagans, idolaters and disbelievers in the Oneness of Allaah; those who worship others along with Allaah or set up rivals or partners to Allaah)”
[Yoosuf 12:108]
Allaah, may He be glorified, praises those who follow that path, as He says (interpretation of the meaning):
“And who is better in speech than he who [says: ‘My Lord is Allaah (believes in His Oneness),’ and then stands firm (acts upon His Order), and] invites (men) to Allaah’s (Islamic Monotheism), and does righteous deeds, and says: ‘I am one of the Muslims’”
[Fussilat 41:33]
It is essential that the one who wants to call people to Islam should have some understanding of that to which he is calling them, but he does not have to know the entire religion, because of the report narrated by al-Bukhaari (3461)
from ‘Abd-Allaah ibn ‘Amr (may Allaah be pleased with him), according to which the Prophet (peace and blessings of Allaah be upon him) said “Convey from me, even if it is one verse.”
Al-Haafiz ibn Hajar (may Allaah have mercy on him) said in Fath al-Baari:
He said in the hadeeth, “even if it is one verse” so that everyone who heard him would hasten to convey whatever he heard of the verses, even if it was very little, so that in this manner everything that he (peace and blessings of Allaah be upon him) brought would be conveyed. End quote.