Sentence:  ... she would distrust him if she saw him again before he had achieved all his promises; had journeyed clear out to the Mississippi ... and had become fluent in <WSD>sermonizing</WSD> in the Dakota language. No, he must see her next in his glory as a practicing missionary. 
Meaning of the word marked with <WSD> tags:  To speak in the manner of a sermon; to preach; to propagate one's morality or opinions with speech.