That was what made sailing possible for Frodo, what made it possible for him to even take hold of the hope for healing.

Do you mean that getting some sense of meaning in what he did in the greater scheme of things (by working on the book), was what made it possible for Frodo to take heart enough to wish to sail? I suppose if he were totally despondent, he wouldn't have bothered; he would just have waited until death and/or madness took him.

Something like that?