Lines 31-37 Summary

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

Yet not to thine eternal resting-place
Shalt thou retire alone, nor couldst thou wish

This is a big turn in the poem. Up until now, we’ve only been talking about the sad and scary aspects of dying. Is the idea of your body turning into oak tree Miracle-Gro comforting? Sure it's better than that claustrophobic coffin, but it's still not great.
Now we get a big "Yet." Even though there’s some bad news about going to our "eternal resting place," the speaker wants us to know that we won’t go there ("retire") all by ourselves.

Couch more magnificent. Thou shalt lie down

In fact, the speaker tells us we’re headed for a "magnificent" and comfy resting place, like a "couch." That sounds pretty good, right? Way better than the "narrow house" we were worrying about in line 12.
We’re making a big swing here, from creepy to comforting.

With patriarchs of the infant world—with kings,
The powerful of the earth—the wise, the good,
Fair forms, and hoary seers of ages past,

The speaker tells us that when we die, we’ll "lie down" with all kinds of fancy and important people.
There will be "patriarchs" (that means fathers, heads of families, or male leaders) from long ago when the Earth was young ("the infant world"). This also makes us think of the Biblical patriarchs, like Abraham.
There will also be kings and others who are "powerful," "wise" and "good."
In this final resting place, there will be beautiful people ("fair forms"). There will also be old ("hoary") prophets ("seers").
Maybe it’s hard to see where this is headed, but he’s building to a point, we promise.

All in one mighty sepulchre. The hills

All of these important people from lines 34-36 will lie down with you in one giant tomb ("sepulcher"). That giant tomb, of course, is the Earth.
That’s what this whole section of the poem is about, the idea that when we die we all lie down together in one big grave. What’s cool is how Bryant can make that sound like a good thing. You're feeling a bit special now, aren't you?