Rambo

Twenty years after the events in Afghanistan, amid the political protests of the crisis in Burma, ruthless military officer Major Pa Tee Tint leads an army of Burmese Army soldiers to pillage small villages in a campaign of fear. He sadistically slaughters innocent villagers and orders teenage boys to be drafted into his army.
Meanwhile, ex-soldier John Rambo now lives in Thailand, where he makes a living capturing and selling snakes as well as taxiing people along the Salween River on his boat. A missionary named Michael Burnett approaches Rambo and hires him to ferry his group into Burma on a humanitarian mission to provide aid to Karen tribespeople. Rambo initially refuses, but another missionary named Sarah Miller persuades him to help them. During their trip, the boat is stopped by Burmese pirates who demand Sarah in exchange for passage. After negotiations fail, Rambo shoots the pirates. Michael is greatly disturbed by Rambo's actions. Upon arriving in Burma, Michael sends him back, claiming they will go on without his help, and that he intends to report Rambo's actions to the authorities. The missionaries are helping a village when the army attack, killing most of the villagers and two missionaries and kidnap the rest, including Michael and Sarah.
When the missionaries fail to return, their pastor asks Rambo to guide a team of five mercenaries to the village where the missionaries were last seen. Rambo agrees and accompanies the mercenaries to the drop-off, where the team's leader Lewis demands he stay at the boat. As the mercenary team arrives at the village, they find it completely destroyed, filled with mutilated corpses. Shortly after, a squad of soldiers show up with a group of hostages and force them to run through a rice paddy with landmines, and betting on the outcome. Outnumbered, the mercenaries take cover, reluctantly planning to wait for them to leave. To their shock, Rambo shows up and singlehandedly wipes out the soldiers with his bow and arrow, allowing the hostages to escape unscathed. Rambo convinces the mercenaries to avenge the villagers and save the hostages at the P.O.W. camp. They infiltrate the camp and rescue the prisoners, including Sarah. They flee, pursued by Tint's soldiers. Rambo manages to get rid of a pursuit team with an unexploded Tallboy bomb from World War II. However, the army manage to capture everyone except for Rambo, Sarah, and the mercenary sniper nicknamed School Boy. As the army prepares to execute the mercenaries and hostages, Rambo hijacks a jeep-mounted machine gun and begins shooting at the soldiers. A firefight ensues and the army suffer heavy casualties. The Karen rebels show up and join the fight, quickly overwhelming the army. Tint, realizing his defeat, attempts to escape the area, but Rambo intercepts and disembowels him.
In the final scene, Rambo, encouraged by Sarah's words, returns to the United States. He walks along an Arizona highway until he sees a horse farm and a rusted mailbox. Reading the name "R. Rambo," Rambo smiles and walks down the gravel driveway as the credits roll.

Question: Why does Michael Burnett approach Rambo and hire him to ferry his group into Burma?
Answer: To provide aid to Karen tribespeople on a humanitarian mission