In the Eileen Elgar letter, Tolkien says Frodo was given grace: first to answer the call, later to resist temptation and endure fear and suffering. But grace is sufficient for the appointed task, not infinite.[2]
The hero is not self-sufficient. The Quest is carried by grace, but grace does not erase struggle. The character is an instrument of Providence, but still must suffer, choose, endure, and act.