I was always puzzled to understand the reason for the extremely abrupt transitions in those Odes of Horace which are meant to be particularly fine.

The "justum et tenacem" is an instance.

All at once you find yourself in heaven, Heaven knows how.

What the firmness of just men in times of tyranny, or of tumult, has to do with Juno's oration about Troy it is hardly possible to conceive.

Then, again, how strangely the fight between the Gods and the Giants is tacked on to the fine hymn to the Muses in that noble ode, "Descende coelo et die age tibia"! This always struck me as a great fault, and an inexplicable one; for it is peculiarly alien from the calm good sense, and good taste, which distinguish Horace.
My explanation of it is this.