This was no playhouse but a house in earnest.
Your destination and your destiny's
A brook that was the water of the house,
Cold as a spring as yet so near its source,
Too lofty and original to rage.
(We know the valley streams that when aroused
Will leave their tatters hung on barb and thorn.)
I have kept hidden in the instep arch
Of an old cedar at the waterside
A broken drinking goblet like the Grail
Under a spell so the wrong ones can't find it,
So can't get saved, as Saint Mark says they mustn't.
(I stole the goblet from the children's playhouse.)
Here are your waters and your watering place.
Drink and be whole again beyond confusion.
The goblet was stolen from a children’s playhouse–an imaginary house as opposed to the “house in earnest.” Frost’s “wholeness” (see final line) thereby encompasses the mental as well as the physical. 
 The goblet is a cheap toy; perhaps a fake spiritual journey is as good as a real one. Or perhaps we are being misled: 
 The road there, if you’ll let a guide direct you  Who only has at heart your getting lost… 
 Alternatively, perhaps the children’s toy reconnects us with something deeper and purer than a “real” goblet could. To the children, with their imagination, it was the Grail. To drink water, which is the source of all life, from a cup that still represents the Grail to you, is to connect with what was lost and become whole again. 

Directive