Dawah means to convey the divine truth to people. The task of conveying requires that you deliver exactly what has come from God, you should neither add to it nor subtract from it. It is a very serious task.
Sahih Muslim, one of the most authentic books of Hadith, tells us that Prophet Muhammad told his Companions that during the last days, a believer would attain a higher level of realisation of religious truths through scientific arguments and convey these truths peacefully to all humanity. This event, in its reality, would be so great that the Prophet observed, “In the eyes of God, this would be the greatest witness in the entire human history.” (Sahih Muslim, Hadith No. 2938)
Thus this greatest witness to humanity is related to the most extraordinary possibilities available in those times. This tradition means that, during the last days, there will appear great opportunities by availing of which it will become possible to perform the most significant role of conveying the divine message ever performed.