That the caller be of good character, religion, and mindfulness of Allah.

The Shaykh : Third: It is necessary that the caller have a religion that drives him to mindfulness of Allah, to doing righteousness, good, and excellence in worship. How many people have called people to Allah by their actions before calling them by their words. Do you know the meaning of this phrase? How many people have called people to Allah by their actions before calling them by their words, meaning that they are of high character and worship, so that people follow their example. There is a caller who calls people with eloquent speech and clear expression, but his action is not as required or not in the required manner. So you find that people do not benefit much from him. They are impressed by his speech when they hear it, but they do not benefit much from him because his action contradicts his speech.
So these are three matters that the caller should, indeed must, possess: knowledge, secondly: intellect, and thirdly: character and righteous action, so that he may be a true caller.