Need a starting point for an explication of Emily Dickinson's "Faith" is a fine invention."
You can start by stating that Faith, to some people, is a real necessity. Although not everyone believes or has a strong system of spiritual belief and guidance, at times having the Faith is sustenance enough for people who have reached a point in their lives where they do not know what to do next. However, one cannot assume that Faith is real, or that it is indeed a resource. All we can safely assume is that Faith, to those who want it, will prevail. Equally, those who choose not to believe in anything will likely find the answers that they seek within their own logic.
Like the allegorical use of the microscope in the poem, faith exists to those who believe in it. Therefore, you can begin your essay by stating that Faith is real to whoever chooses to have it, and that those who do believe and choose to have faith, or follow a Faith, will find the answers that they are looking for within themselves.