Frost's speaker admits something many people do: we protect ourselves with jokes and teasing, building a private space behind "light words." But that hiding comes with a cost. The heart is "agitated" until someone sees through the act and finds us "really out." We want to be discovered, even while we work to avoid it.
The second stanza turns slightly rueful. It's a pity, the speaker says, if we finally have to say things plainly, in the "literal," just so a friend will understand us. The phrase "or so we say" hints that this reluctance may be partly an excuse.
The last stanza widens the idea. Children playing hide-and-seek and even God "afar" are put in the same position: anyone who hides too well must eventually speak up and say where they are. The mood is gentle, wry, and a little tender. The poem sounds amused at our evasions, but it also understands the loneliness behind them.