A dayee is like a beacon standing by the roadside as a divine guide for the wandering caravan of humanity. The Quran says: ‘Worship God alone and shun the evil one.’ (16:36) In another chapter, it records the words of the Prophet: “… hasten to God; truly, I am sent by Him to give you a clear warning” (51:50). This is the real point of calling people to God is to warn people to seek out God and shun Satan.
In this world, a man stands in between two calls: one is God’s call, and the other is Satan’s. God is the source of all goodness and calls people toward all that is good. On the contrary, Satan is the source of all evil and calls people towards it. The test of a man is that he should not fall prey to Satan’s illusion: he should instead leave Satan and run toward God.
Source: Dawah Made Simple