Some explain this for me. How can Djokavic automatically move up to rank 1 even if Nadal beats him on Sunday?

At the start of the tournament, Novak had 12,005 points and Nadal had 12,070 points. If Nadal wins Wimbledon, he will still have 12,070 points, but if he loses, his tally will go down. Novak was defending a semi final spot from last year so by making the finals he has gained a few hundred points already, so even if he loses in the final, he will have greater than 12,070 points and hence he will be #1 on Monday.