"Faith" is a fine invention
When Gentlemen can see—
But Microscopes are prudent
In an Emergency.
These lines show Dickinson’s belief that faith alone will not save a person. We need the tools humans have created when in an emergency. This poem shows how Dickinson did not believe faith would save her in a time of crisis (doubt). 
 This whole poem shows that Dickinson was conflicted in her beliefs. In other poems she tells of Heaven and God saving her, yet in this poem she says faith is an invention. This poem shows the side of Dickinson that doubted faith and God.
Faith is a fine invention