Gentle speech in inviting others to the truth is one of the causes of its success; because it does not provoke arrogance from sin, nor does it stir up the false pride that tyrants live by. Instead, it awakens the heart, draws it in, moves it, and reminds it.
Yahya ibn Mu'adh Rahimahullah said:
إلهي! هذا رفقك بمن يقول: أنا الإله، فكيف رفقك بمن يقول: أنت الإله؟ وهذا رفقك بمن قال: ﴿أنا ربكم الأعلى﴾ ، فكيف بمن قال: سبحان ربي الأعلى؟
My Lord! This is Your gentleness with the one who says, "I am the god," so how would Your gentleness be with the one who says, "You are the Allah"? This is Your gentleness with the one who said, "I am your supreme Lord" (referring to Fir'awn), so how would it be with the one who says, "Glory is to my Lord, the Most High" (referring to the believer)?