The first word of this line tips us off that Dickinson is using simile. A simile is a way to compare one thing to another, using "like" or "as." It looks like we're only getting the first bit of it on this line, though. We'll have to keep reading to see how the comparison unfolds.
For now, what we do see are more capped words—"Lightning" and "Children." Looks like they're VIPs in a poem about truth, too, but we can't be sure why just yet. Onward, Shmoopers.
With explanation kind
Now we have the full comparison before us. Dickinson compares how telling the truth in a delicate (and slant) way can make it easier for us to handle is just like how explaining what lightning is and how it works can take the fear out of it for children.
There's also a comparison within a comparison thing happening here. Dickinson's comparing the truth to lightning. Lightning is powerful, bright, beautiful—and also a little terrifying sometimes. Dickinson thinks the truth has a lot of the same stuff going on.
She's also comparing the "us" in the poem (presumably a universal "us," as in all of us, even your Aunt Tillie) to children.
Children are sometimes considered innocent (well, maybe until you've actually hung out with a two year old and seen how much damage they can really do), sensitive, and easy to overwhelm. We can see the likeness to "us" and children in the third line with "infirm Delight." We're fragile, too, not unlike children sometimes, especially when it comes to super-powerful things like the Truth.
Truth, here, needs to be dished out in an even-handed way, the way you would hold a child's hand through a mini-lecture on lightning.
The Truth must dazzle gradually
If the truth is as powerful as this poem says it is, it's best not to take it all in at once, but instead as Dickinson advises, gradually. Think about some crazy hot sauce. A drop is delicious, but it's powerful. There'd be no way you could take down an entire bottle in a sitting. The truth is kind of like hot sauce that way: tasty, but in small doses.
"Dazzle" has two definitions that make sense in this context. The first is to amaze. The truth is definitely capable of being amazing, especially in this poem where it's put on quite the pedestal. The second definition of "dazzle" is to temporarily blind—you might be dazzled by headlights, or a massive diamond. The truth, in this poem, has been compared to lightning (which, if you stand too close, is also dazzling), so this definition works, too.
Or every man be blind—
There you go. If you take the truth in all at once (or if someone gives it to you all at once), you'd be over-dazzled and go blind.
Okay, so maybe you wouldn't actually go blind, but it would be way too much to take in. You'd be bowled over by its awesome be-dazzling power. Boom.
In order for us sensitive humans to "handle the truth" (as Jack Nicholson would say) it needs to be doled out in small bits, and delicately, maybe even in a circuitous way.
Dickinson ends this poem, like many of her others, with a dash rather than a more final punctuation mark, like a period. We'd say that this gives the poem a sense of continuation. When you use a period, you're shutting the door. The dash suggests that we can keep it open. We can keep talking about the poem, the truth, whatever. Emily Dickinson was kind enough not to slam the door in our faces, just like she was kind enough not to zap our eyeballs out with some super-awesome Truth bolts.