Stanza 5 Summary

Get out the microscope, because we’re going through this poem line-by-line.

Lifting the valleys of the sea
my father moved through griefs of joy;

Whoa, check it out: we've got our first capital letter of the poem so far, which really lifts the word "Lifting" from the poem and emphasizes the idea.
We also dive into some more nature imagery here when the speaker talks about his father "Lifting the valleys of the sea." (We guess the father wasn't that concerned with saving the whales.)
This image brings us back to the idea of the father raising the spirits of those around him.
It also seems to be playing with the mountain imagery from the previous stanza.
In the next line, Cummings echoes his first stanza by bringing back the whole "moved through" thing. This time, however, the father is moving through "griefs of joy," which sounds very similar to "dooms of love" to us.
The speaker could be saying that his dad dealt with happiness, sadness, and everything in between.

praising a forehead called the moon
singing desire into begin

The speaker is once again aligning his father with something that's high in the air.
Before he was listening to mountains and raising sea valleys, now he's praising the moon. (Maybe his father was a werewolf?)
It's interesting that he describes the moon as a "forehead." Is it possible that the speaker is equating the moon with human thought with this description? Get it? "Forehead" = the brain that lurks behind it (that's called metonymy in the poetry biz).
Maybe the speaker is saying that his father was always pushing himself intellectually.
With the last line of the stanza, we hear more about the father's singing. (Man, this guy really ought to get on The Voice or something.)
This time, instead of singing morning out of night, he's singing "desire into begin."
It sort of sounds we're going back to that whole thing about inspiring people here.
The father shows people how to stop wanting to do something, and he helps them to get started already.