Horace was perfectly at liberty to choose his own subjects, and to treat them after his own fashion.

But he confounded what was merely accidental in Pindar's manner with what was essential; and because Pindar, when he had to celebrate a foolish lad from Aegina who had tripped up another's heels at the Isthmus, made all possible haste to get away from so paltry a topic to the ancient heroes of the race of Aeacus, Horace took it into his head that he ought always to begin as far from the subject as possible, and then arrive at it by some strange and sudden bound.

This is my solution.

At least I can find no better.

The most obscure passage,--at least the strangest passage,--in all Horace may be explained by supposing that he was misled by Pindar's example: I mean that odd parenthesis in the "Qualem Ministrum:" quibus Mos unde deductus per omne--.
This passage, taken by itself, always struck me as the harshest, queerest, and most preposterous digression in the world.