Stanza 3 Summary

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

Therefore, since the world has still
Much good, but much less good than ill,

These lines start a new stanza and mark a shift in the poem. Terence has turned away from his praise and criticism of beer, and he's about to explain why he went on that tangent. He's slowly moving back to his defense of sad poetry, which is the reason he got started on all this in the first place.
Basically, his point is that there's good in the world, but there's definitely more bad that good ("much less good than ill"). So maybe we shouldn't look at the world through a fake-happy haze of beer.

And while the sun and moon endure
Luck's a chance, but trouble's sure,

Basically, this line means that there's always going to be trouble. We might have good luck sometimes, but we can count on bad luck. Terence turns out to be kind of a pessimist, doesn't he?
We think it's important that Terence wraps up this bad news in a kind of folksy little saying, like a proverb. It all fits with the country barroom setting of this poem. He's got a serious message, but he knows his audience, too. He's not going to roll out his ideas like a college professor.

I'd face it as a wise man would,
And train for ill and not for good.

Terence thinks it's best to face the world the way it is—not like a drunken fool, but like a "wise man." Since the world is mostly bad and full of trouble, he figures it's better to prepare ("train") for bad things rather than good ones.

'Tis true, the stuff I bring for sale
Is not so brisk a brew as ale:

Here Terence makes an analogy between beer and poems, and admits that the metaphorical poetic "brew" he's offering isn't as exciting and enlivening ("brisk") as beer is.

Out of a stem that scored the hand
I wrung it in a weary land.

This is kind of a complicated image, but we'll do our best to break it down. Basically, Terence is keeping up the analogy between writing poems and brewing beer. Beer comes from grain, like wheat or barley. So Terence imagines himself squeezing his poetry out of a plant (a stem) that cut ("scored") his hand while he "wrung" (that's an old word for squeezed) it.
He squeezes out this weird poetry juice in a "weary land." The whole feeling of this stanza has turned pretty grim. The beer-drinking and good times in the last stanza seemed pretty happy, but now the world of poetry and writing seems a lot harsher and sadder.

But take it: if the smack is sour,
The better for the embittered hour;

Now Terence really gets going on his defense of poems. He orders the guy he's talking with to "take it" (the poetry, that is).
That command is followed by a colon (the punctuation mark, guys, not the lower part of your digestive system), and a little pause (known as a caesura). That helps us to focus on the change in the poem. Now Terence is fully in control, and he's telling us what to do.
His logic goes like this: He admits that the taste ("smack") of poetry is "sour" (he's keeping up the "poetry as beer" analogy).
Still, he thinks that something sour is a better match for the sadness of life that he's been talking about ("the embittered hour").

It should do good to heart and head
When your soul is in my soul's stead;

Terence promises his buddy that this sour-tasting poetry will be good for his "heart and head" when his friend is feeling as bad as he does. It sounds like Terence is in rough shape, but it also seems like poetry helps to soothe his "soul."

And I will friend you, if I may,
In the dark and cloudy day.

Terence promises to "friend" this other guy when times are rough. It kind of sounds like he wants to add him on Facebook, but we promise you this is solidly pre-Internet. He just means that he and his sad poetry will be a source of support when things seem "dark and cloudy."