The phrase "sharpening my oyster knife" in paragraph six of "How It Feels to Be Colored Me" primarily conveys eagerness and excitement at the opportunities afforded by life. Hurston's phrase is an extension of the metaphor of the world as an oyster, which dates back at least as far as Shakespeare. In The Merry Wives of Windsor, Pistol says:

Why then the world's mine oyster
Which I with sword will open.

The idea is that the world is first of all something to be enjoyed and also that, while it may take some effort to open, everything good it has to offer is there for the taking.

The image is typical of Hurston's essay, which is positive and enthusiastic in turn. She says that she is too busy sharpening her oyster knife to "weep at the world," suggesting that her intellectual opponents are preoccupied with misery and injustice, at the expense of appreciating life. While Pistol says that he will open his oyster (rather dramatically) with a sword, Hurston is more precise in her approach, naming a smaller and more modest implement which, nonetheless, is exactly the right tool for the job. The reference to sharpening the knife suggests that she will be well prepared to extract the maximum amount of value and relish from the world.