http://starwars.wikia.com/wiki/Invasion_of_Naboo

Valorum and the Council dispatched two Jedi, Qui-Gon Jinn and his Padawan, Obi-Wan Kenobi, to meet with the Federation Viceroy and ensure the Federation's withdrawal from the system.

Basically, they were doing what Jedi ALWAYS did - serving as diplomats and conflict resolution negotiators. They were acting in official capacity as Ambassadors for the Supreme Chancellor Valorum (from the TPM script):

CAPTAIN : ... the Ambassadors for the Supreme Chancellor wish to board immediately.

The reason they were sent to talk was because the blocade of Naboo was basically a small move in a large chess game between Trade Federation and Republic over trade route taxation.

http://starwars.wikia.com/wiki/Invasion_of_Naboo

Valorum and the Council dispatched two Jedi, Qui-Gon Jinn and his Padawan, Obi-Wan Kenobi, to meet with the Federation Viceroy and ensure the Federation's withdrawal from the system.

Basically, they were doing what Jedi ALWAYS did - serving as diplomats and conflict resolution negotiators. They were acting in their official capacity as Ambassadors for Supreme Chancellor Valorum (from the TPM script):

CAPTAIN : ... the Ambassadors for the Supreme Chancellor wish to board immediately.

The reason they were sent to talk was because the blockade of Naboo was basically a small move in a large chess game between the Trade Federation and the Republic over trade route taxation.