The Question and Answer section for Matthew Arnold: Poems is a great resource to ask questions, find answers, and discuss the novel.
The speaker warns that the scholar-gipsy should avoid everyone who suffers from the "disease," of man lest he become infected as well. Arnold feels weighed down by the responsibilities of life. He wishes, like the scholar Gipsy, he could escape...
Sorry we cannot write introductions in this short-answer forum.
Undiscovered mysteries are those things that happen after death.... the unknown. For the speaker, what happens after death is an unknown entity.
The future and its viewless things –
That undiscovered mystery