It breaks down like this:
If I have told you earthly things
And you do not believe,
In my note to myself, I said that I didn't know if this feature was present in the Greek or whether it has any significance.How can you believeIf I tell you heavenly things?
The Daily Dose of Greek went over this verse last month, and I learned that this chiasm isn't present in the Greek. It's a feature unique to the English translation.