Extensive knowledge of military affairs: his training began from a very young age. From school age he was part of his father’s army, then lead the greatest army as commander himself from the earliest boyhood. All first-hand experience.
Virtue: courage - credited by Sulla for winning the Civil War with arms/good organisation. War against pirates was dangerous, foul, long-standing, but he was still determined to put an end to it.
Prestige/Military track record: Servile war against Spartacus was put to an end purely by the rumour of his name and arrival. Pirates War - people were having to live with impossible conditions for sailing, either the dangerous winter weather or sea infested by pirates. Praetors kidnapped, famous ports such as Caietae and Colophon plundered, merchants cannot trade - extent of the pirates’ trouble. Pompey cleaned out the whole Mediterranean and was quick (from seeing them at Ostia to not hearing of them anywhere). Despite shortage of corn supply, dramatic drop in prices when he was appointed against pirates - faith of people.
Respected by foreigners: seen as godlike. Embodies good Roman qualities - restored the name for Rome - previous commanders brought shame to Rome’s reputation for their greed and inefficiency. Pompey is the opposite - even his enemies admire his compassion more than they fear his courage.
Moral virtue/integrity: unlike other commanders, he is not greedy. He does not sell commissions, invest public money for own profit, use public funds to bribe officials to prolong his commands. His army do not cause calamities like others’ in the past have - if a man cannot restrain his own greed, he cannot control his army, Pompey can - good reputation amongst allies.
Speed: Secured corn supply in Sicily, Africa and Sardinia. Annexed Cilicia in 49 days, secured Italy, Spain, Transalpine Gaul, all of Greece and Illyrian sea. Made preparations in winter, began in spring and finished midsummer.