A.T. Robertson Commentary Acts 25:21

"But when Paul had appealed to be kept for the decision of the emperor, I commanded him to be kept till I should send him to Caesar." — Acts 25:21 (ASV)

When Paul had appealed (του Παυλου επικαλεσαμενου). Genitive absolute with first aorist middle participle of επικαλεομα, the technical word for appeal (verses 11,12). The first aorist passive infinitive τηρηθηνα (to be kept) is the object of the participle.

For the decision of the emperor (εις την του Σεβαστου διαγνωσιν). Διαγνωσιν (cf. διαγνωσομα 24:22, I will determine) is the regular word for a legal examination (χογνιτιο), thorough sifting (δια), here only in N.T. Instead of "the Emperor" it should be "the Augustus," as Σεβαστος is simply the Greek translation of Augustus, the adjective (Revered, Reverent) assumed by Octavius B.C. 27 as the αγνομεν 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 Σεβαστος has the notion of worship (cf. σεβασμα in Acts 17:25). In the N.T. only here, verse 25; 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 (εως αν αναπεμψω αυτον προς Καισαρα). Here αναπεμψω can be either future indicative or first aorist subjunctive (identical in first person singular), aorist subjunctive the usual construction with εως for future time (Robertson, Grammar, p. 876). Literally, "send up" (ανα) to a superior (the emperor). Common in this sense in the papyri and Koine writers. Here "Caesar" is used as the title of Nero instead of "Augustus" as Κυριος (Lord) occurs in verse 26.