Lines-10-18 Summary

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

and if I had written anything else at the top
of the examination form where it said college

Our speaker is back! The "I" reemerges. We should celebrate, right? Let's find out…
Don't put your party hats on too quickly. We have another "if," and this one has no connection so far for the ones before it.
Somehow, whatever our speaker wrote on top of this college entrance exam is important enough to include alongside all these other mini-histories.
Unfortunately, we're going to have to wait to find out why it's important, because the speaker is really keeping us in suspense. Fiddlesticks. Why do you think that is?

of your choice or if the questions that day had been
put differently and if a young woman in Kittanning

The exam seems to have had something to do with where our speaker ended up at college.
This is our first clearly personal significant event of his past that our speaker has let us in on. So far, we still don't know why he's mentioned all the other stuff about the red-haired boy and the war.
We thought for a second that, with the reemergence of the "I," our speaker was going to spill the deets. No soup, though. Instead, it looks like he's off in yet another direction, telling us about a young woman in Kittanning.

had not taught my father to drive at the age of twenty

Ah, so now we're back to the personally significant. The woman in Pennsylvania was the speaker's father's driving instructor (if you can follow that).
20 is pretty late to be learning how to drive, especially when you consider that, back in the day (when the speaker's dad was growing up), kids often learned to drive even earlier than we do now.
Maybe the father's driving lessons (late as they were), ended up being somehow important to our speaker.

so that he got the job with the pastor of the big church
in Pittsburgh where my mother was working and if

Ah-ha! Mother meets father. This is absolutely significant to our speaker. After all, his parents had to meet in order for him to be born, right?
So the driving lessons enabled his father to leave town to get a job in "the big church" in a bigger city—Pittsburgh.
Look out, though. At the end of line 16, Merwin throws in another "if." He's really piling them up on us!

my mother had not lost both parents when she was a child
so that she had to go to her grandmother's in Pittsburgh

Man—there's a lot of dying in this poem: first the soldier, then his brother, and now the speaker's maternal grandparents.
So, the speaker's father ends up in Pittsburgh for a job, and his mother moves there as a kid to live with her grandparents.
Without exactly saying how his parents met, the speaker tells us about the outside forces that drew them together.