uno loco, 'in one point'
serviunt, 'become slaves.'
possis is the apodosis of a conditional sentence with the protasis suppressed. 'You would not be able (if you were to try),' i.e. 'you can never hope to be able.'
neque ulla, etc. This hope was not realized. The immediate danger being removed, the equites fell back into their habitual attitude of opposition to the senate.
pro imperio, 'in the place of military command.' The imperium was the authority vested in a general in virtue of which he controlled his army by martial law. It belonged equally to all the higher magistrates, but within the walls of Rome itself its exercise was restricted. Cicero was not going to govern a province, and therefore not to command an army.
pro provincia. Sulla had ordained that each of the ten chief magistrates (two consuls and eight praetors) should, after the expiration of his year of office in the city, govern a province as proconsul or propraetor. The senate decided which should be the consular provinces, and the consuls settled between themselves (by lot or otherwise) which each should take. The consular provinces for 62 b.c. were Macedonia and Cisalpine Gaul. As Macedonia was a rich province, Cicero had given it up to Antonius, in order to secure his support against the conspirators. His own province would therefore in the ordinary course have been Cisalpine Gaul. But subsequently he asked to be allowed to resign it, and it fell to the praetor Metellus Celer. (See Ep. ad Att. 2. 1 'cum provinciam in contione deposui,' and ad Fam. 5. 2, where writing to Metellus Celer he says 'si hoc dicam, me tui causa praetermisisse provinciam, tibi ipsi levior videar esse.') By resigning his province he gave up the command of an army, and with it the chance of a triumph.
pro clientelis, etc. Provincial communities often attached themselves as 'clients' to their former governors, who became their 'patroni' and were specially bound to look after their interests. Cicero here says that by giving up a province he has given up the best opportunities of forming such connections; nevertheless though confined to the city he will still do his best in that direction. Tr. 'In the place of ties of clientship and mutual friendship with provincials, which nevertheless by such influence as I can exercise in the city (urbanis opibus) I strive to acquire as zealously as I maintain them' (when acquired).
pro meis, etc. Note that 'pro' is here used in a different sense from the foregoing; 'in return for my zeal,' etc.