Is it necessary to memorize the entire Qur'an first before inviting people to the religion, especially with existing reading difficulties?

Calling to Allah is a noble and great mission. One can be a caller to Allah Almighty without the condition of memorizing the entire Holy Quran, but it is important to begin by memorizing it completely. For the Quran is the origin of knowledge, and memorizing it helps in understanding it and understanding the Sunnah.