A.T. Robertson Commentary Acts 23:16

"But Paul`s sister`s son heard of their lying in wait, and he came and entered into the castle and told Paul." — Acts 23:16 (ASV)

Their lying in wait (την ενεδραν). Old word from εν (in) and εδρα (seat), ambush. In N.T. only here and 25:3. Accusative object of ακουσας.

He came (παραγενομενος). Second aorist middle participle of παραγινομα. It may mean, "having come upon them" and so discount their plot, a graphic touch. Vincent thinks that some Pharisee, since Paul was a Pharisee and so a member of the "guild," told his nephew of the plot. Perhaps, and perhaps not.

Told Paul (απηγγειλεν τω Παυλω). This nephew is not known otherwise. He may be a student here from Tarsus as Paul once was. Anyhow he knows what to do when he catches on to the conspirators. He had enough address to get into the barracks where Paul was. He ran the risk of death if discovered.