At stake for Nadal is a 7th French Open title, a mark that would make him the greatest French Open champion in terms of title counts, as the Spaniard is currently tied at six with Bjorn Borg. At stake for Djokovic is his first French Open title. However, with a win, the Serb would earn a career Slam as he has won each of the other majors at least one time.
The World No. 1 ranking is not at stake in the match–at least not directly. Djokovic will be the World No. 1 player following the French Open even if he loses the final as he has been the most consistent player in the last 52 weeks. However, if Nadal hopes to catch Djokovic for the top spot in the longer term then defending his title at Roland Garros will certainly help. That said Djokovic will increase his points lead in the rankings in all cases as his final appearance is a round better than his 2011 semifinals appearance.
Heads up Nadal has the winning record against the Serb at 18-14 and the World No. 2 appears poised for the title once again. Unlike Djokovic, Nadal has brushed aside all who have stood in his way at Roland Garros and that includes his semifinals opponent David Ferrer, a player who is highly respected on clay but one that looked outclassed by Nadal on Friday.
Djokovic has had plenty of trouble advancing to the final although he did make light work of former champion Roger Federer. The Serb saved several match points against Jo-Wilfried Tsonga in the quarters and even Andreas Seppi put a fright into Djokovic after taking a two sets to love lead in the fourth round.
Nadal is by no means a lock against Djokovic, but based on Rafa's two recent clay court victories over the Serb, Nadal's history of success at the French Open, and Djokovic's near misses to weaker competition surely Nadal's status as favorite is justified (ie. bet365). I'm not convinced that Djokovic can even take a set off of Nadal as the World No. 2 has looked scary at Roland Garros this season.
Prediction: Nadal straight up.