Narragansett people
Arnold was the only member of the colony besides Roger Williams who was highly proficient in the Narragansett and Wampanoag tongues, and he was often called upon to interpret during negotiations. In June 1645, he was sent by the General Court of Massachusetts to the Narragansett people to urge them to desist from engaging in a war with the Mohegans. On 28 July, Arnold and two others were sent to get the hostile tribes to send deputies to Boston to talk and make peace. This attempt failed and, a month later, Arnold would not go back again, as he had been charged with misrepresenting the reply of the tribes, and Roger Williams went as interpreter in his place.