It matters the subject or requirement. Learning can be good when you are learning something big and important and learning can be bad when learning bad habits and more. Hope this answers your question :D
It is usually stated in overt terms and often changes throughout the poem. The correct answer should be "It is not always stated overtly and is understood only by reading the whole poem". This is correct because the theme usually does not change itself, but there can be multiple themes analyzed.
It is an adjective. Left-hand is describing the kind of side.