There has already been a manifest sign (of the truth of God’s way) and lesson for you in the two hosts that encountered (at the Battle of Badr): one host fighting in God’s cause, and the other disbelieving, who saw with their very eyes (the host of the believers) as twice their actual number (during fighting). God confirms with His help and victory whom He wills. Surely in that is a lesson for those who have the power of seeing.