Gamaliel is a well known figure in the first century. He was likely the grandson of the famous Hillel and is mentioned in the Mishnah. He was active after A.D. 25 and was reputed to have been a great teacher of the Law. One problem is that he is often confused with Gamaliel II, who lived after the fall of Jerusalem.
Gamaliel urges careful deliberation before acting. It may be that they are worthy of death, but one must think about what the ramifications of another execution of a messianic pretender. He refers to two other “messianic pretenders” which gathered some following but eventually came to nothing. Each of these men are known from Josephus as rebels against Rome who had humble origins, developed a bit of a following, and were eventually killed.
Theudas is known from Josephus, Antiq. 20.5.1 §97-98. In this passage, Theudas led a revolt during the reign of Fadus, A.D. 44-46. This is obviously a problem, since Gamaliel is giving this speech at least ten years before Theudas rebelled. This problem is usually explained by noting that the name Theudas is a common name in first century inscriptions. In addition, the period after the death of Herod the Great saw many rebellions, so it is likely that Gamaliel refers to a leader of one of these earlier rebellions. Judas the Galilean lead a tax-revolt about A.D. 6, described by Josephus in Antiq 18.1.6, §23. Like Theudas, he died and his followers dispersed.
His point in referring to this recent history is that if God was really behind any of these messianic movements, then their leaders would not have been executed. Perhaps there is a backwards warning to Peter and his followers as well: If your leader is really dead, maybe you ought to stop this preaching. On the other hand, his warning is also to the Sadducean leader of the Sanhedrin: if you are wrong about this, you will be fighting God! To a certain extent, Gamaliel’s advice is a nit of “shrewd popular politics” which endorses neither side’s view of who Jesus was (Dunn, Beginning in Jerusalem, 174, n. 14).
Gamaliel’s conclusion is that a messianic movement which is from human origin is doomed to fail; but if it is of divine origin it is destined to succeed. It would be better to let the disciples of Jesus do as they please rather than to “fight against God.” The examples given came to nothing, in both cases the leader was dead. If Jesus is dead, then his followers will disappear as well – but only if they are no longer persecuted.
This advice is wise because the best way to solidify a religious movement is to persecute it. There will be no half-hearted followers of Jesus if there is persecution. By encouraging peace with the growing messianic movement, Gamaliel may have opened the door to some of the problems which develop over the next few years as the messianic movement begins to evangelize Gentiles.