"As our Indians perceive that much honour is accorded to the missionaries, and that they have given themselves in respect and reverence the title of Patriarch, some of these barbarians have often been seen meddling with, and affecting to perform, the office and functions of missionary, even to hearing confession, like us, from their fellow countrymen" Can someone explain this passage to me ?

This passage means that the Indians are imitating the missionaries and are doing what the missionaries are doing because they like the honor and respect that is given to the missionaries.

They have begun calling themselves by the title of Patriarch and are even seen hearing confessions from their fellow Indians like they have seen the Reverends among the missionaries do and the writer finds this behavior distasteful