When Paul had appealed (tou Paulou epikalesamenou). Genitive absolute with first aorist middle participle of epikaleomai, the technical word for appeal (Act 25:11, Act 25:12). The first aorist passive infinitive tērēthēnai (to be kept) is the object of the participle.
For the decision of the emperor (eis tēn tou Sebastou diagnōsin). Diagnōsin (cf. diagnōsomai Act 24:22, I will determine) is the regular word for a legal examination (cognitio), thorough sifting (dia), here only in N.T. Instead of “the Emperor” it should be “the Augustus,” as Sebastos is simply the Greek translation of Augustus, the adjective (Revered, Reverent) assumed by Octavius b.c. 27 as the agnomen that summed up all his various offices instead of Rex so offensive to the Romans having led to the death of Julius Caesar. The successors of Octavius assumed Augustus as a title. The Greek term Sebastos has the notion of worship (cf. sebasma in Acts Act 17:25). In the N.T. only here, Act 25:25; Act 27:1 (of the legion). It was more imposing than “Caesar” which was originally a family name (always official in the N.T.) and it fell in with the tendency toward emperor-worship which later played such a large part in Roman life and which Christians opposed so bitterly. China is having a revival of this idea in the insistence on bowing three times to the picture of Sun-Yat-Sen.
Till I should send him to Caesar (heōs an anapempsō auton pros Kaisara). Here anapempsō can be either future indicative or first aorist subjunctive (identical in first person singular), aorist subjunctive the usual construction with heōs for future time (Robertson, Grammar, p. 876). Literally, “send up” (ana) to a superior (the emperor). Common in this sense in the papyri and Koinéš writers. Here “Caesar” is used as the title of Nero instead of “Augustus” as Kurios (Lord) occurs in Act 25:26.