What does Acts 5:36 mean?

Gamaliel, a most-respected scribe of the Pharisees, is trying to calm the Sanhedrin. Sadducees in the group are bent on killing Jesus' apostles. The Sadducees were perturbed when the apostles taught that Jesus rose from the dead. Now, the apostles insist that Jesus is the Jewish Messiah, that God raised Him, and that He is sitting at God's right hand (Acts 5:30–33). And, they say, it was the Sanhedrin who killed Him!

Gamaliel points out that this isn't the first time some wayward Jew, "claiming to be somebody," gathered a following and then disappeared from history. His mention of Theudas, however, is puzzling at first. The only Theudas remembered by history was active in AD 45. Even if Jesus was crucified later than AD 33, and even if the apostles were active in Jerusalem for years, this trial still occurs before that Theudas came on the scene. Gamaliel says Theudas precedes Judas the Galilean who "rose up in the day of the census"—which was the time Jesus was born (Luke 2:1–2; Acts 5:37). Logically, this must be a different Theudas than the one Josephus the historian mentions. "Theudas" is Greek for "God-given"; it's very possible the name is pseudonymous.

The scribe's point is that the Sanhedrin doesn't have to risk political ruin. The fact that history has no memory of this other Theudas is somewhat the whole point Gamaliel is making. Like Theudas and Judas the Galilean, if God isn't behind a movement, He will dissolve it eventually. This line of thinking isn't perfectly consistent with God's intentions for the leaders He places over His people, but it serves the apostles well enough. Instead of executing the Twelve, the Sanhedrin beats them and lets them go (Acts 5:40).