The praetorian guard was the emperor's personal bodyguard, and since Paul by his appeal had placed himself at the emperor's disposal, it was natural that the soldiers who had charge of him in his lodgings, relieving one another in succession, should be drawn from the praetorian guard. Few of those soldiers had ever come across a man like Paul before, and each of them would quickly learn what had brought him to Rome. The Romans didn't look at imprisonment as punishment, but as confinement awaiting trial. Arndt and Gingrich note that before NT times it was only used in Aristotle, where it denotes a self-seeking pursuit of political office by unfair means. Politics don't seem to have changed much over the millenia.
Most progress seems like it comes through that painful process.
19 gives intercessory prayer as a cause for Paul's hope. And because of this I rejoice.