Abraham does not say Just wait until the gospels and epistles are written, or after the Resurrection. That should help them. Rather, he points then to the Old Testament itself the Law and the Prophets. Dives argues that the Old Testament Revelation is not enough. He says his surviving brothers need a sensational, fantastic miracle.
Some modern people suggest the same thing.
Dives conjures up the most difficult, indisputable miracle and says, If someone from the dead goes to them, they will repent. But another Lazarus in John 11 had done just that and the result, rather than increased belief, was increased opposition. The Father also knew that Christ would soon be resurrected and yet many would not believe. People with hardened hearts are not converted, even with miracles. The principle laid down in these words is of deep importance.