The Gospel is enlightenment and no-one here has ever said it is anyone other than God who informs the person as to his state (sinner) and his need (salvation).
You do God a disservice by suggesting He can deliver the Gospel but can't make a man understand what he's hearing. It is either received or it is rejected but God's grace has been effectual in what He set it out to do. To those who believe, more grace is given to effect salvation. To those who don't believe, no more grace and they remain dead in their sins.