The fact that the Eastern Orthodox have a historical tradition affirming this is no small approbation. The Eastern Orthodox are very good (not perfect but very good) custodians of traditions.
Why else would I think that Rabbi Gamaliel could *possibly *have been a Christian?
Recall when the Sanhedrin put St. Peter and the Apostles on trial, St. Peter actually put the Sanhedrin on trial.
Then the Sanhedrin (on the orders of Rabbi Gamaliel) had them removed for a while. Yet someone knew enough to relate what happened to St. Luke much later so Luke could write it down in the book of Acts.
ACTS 5:34 34 But a Pharisee in the council named Gamaliel, a teacher of the law, held in honor by all the people, stood up and ordered the men to be put outside for a while.
Was it Gameliel who told the Apostles what happened in their absence while being whisked away from the Sanhedrin during their deliberation? We don’t know. It could have been.
Maybe this knowledge of what occurred with the Sanhedrin was infused by God. Or, St. Paul may have been there as a member or “job shadowing” with Gamaliel whom he studied under (Acts 22:3). St. John the Evangelist was possibly even related to the High Priest (John 18:15) and perhaps it was him (the high Priest himself) or Nicodemus or Joseph of Arimathea or someone else that explained to the Apostles what went on with the Sanhedrin in the absence of the Apostles. . . . but possibility it was Gamaliel himself.
ACTS 5:29-34 29 But Peter and the apostles answered, "We must obey God rather than men. 30 The God of our fathers raised Jesus whom you killed by hanging him on a tree. 31 God exalted him at his right hand as Leader and Savior, to give repentance to Israel and forgiveness of sins. 32 And we are witnesses to these things, and so is the Holy Spirit whom God has given to those who obey him." 33 When they heard this they were enraged and wanted to kill them. 34 But a Pharisee in the council named Gamaliel, a teacher of the law, held in honor by all the people, stood up and ordered the men to be put outside for a while.
The book of Acts also tells us Rabbi Gamaliel was instrumental in sparing the lives of the Apostles. Listen to the words of Gamaliel . . .
ACTS 5:35-40 ** 35 And he said to them, "Men of Israel, take care what you do with these men. 36 For before these days Theudas arose, giving himself out to be somebody, and a number of men, about four hundred, joined him; but he was slain and all who followed him were dispersed and came to nothing. 37 After him Judas the Galilean arose in the days of the census and drew away some of the people after him; he also perished, and all who followed him were scattered. 38 So in the present case I tell you, **keep away from these men and let them alone; for if this plan or this undertaking is of men, it will fail; 39 but if it is of God, you will not be able to overthrow them. You might even be found opposing God!" 40 So they took his advice, and when they had called in the apostles, they beat them and charged them not to speak in the name of Jesus, and let them go.
WHY would the Jews of the Sanhedrin NOT know if Gamaliel were among the Jews of the Christians?
Well if that were public knowledge what would happen to Gamaliel (and probably his family)?
I think Acts 5:33 gives us good insight to the consensus among the Sanhedrin members.
ACTS 5:33 33 When they heard this they were enraged and wanted to kill them.
What do you think would occur if the Sanhedrin was aware of Gamaliel being a fulfilled Jew (a Christian)?
Rabbi Gamaliel would have to work among them in secret or not only merely be himself martyred, but cause the deaths of many other Jewish Christians too.
Why have Gamaliel stay there in the Sanhedrin?
Recall there was a persecution of the fulfilled Jews (Christians) by the Jews of the Sanhedrin. The information they could get from Gamaliel may have saved many Jewish Christian lives. Gamaliel was highly thought of by the Sanhedrin and even by Rabbinic Jews today. Rabbinic Jewish tradition states (Sotah 15:18):
"Since Rabban Gamaliel the Elder died, there has been no more reverence for the law, and purity and piety died out at the same time"
Possibly this question of a secret Christian among the Sanhedrin being raised is one reason why the rabbis later, after the destruction of the Temple, eventually instituted curses against some of their fellow Jews (Jews who become Christians, whom the rabbis wrongly considered heretics). This curse is "prayed" to this very day in the Amidah (Shemoneh Esrei) in "prayer" number 12.
It would have been against our faith for any Jewish Christian to pray an anti-blessing or an anti-benediction or a malediction (a curse) against any fellow Jews or even anybody else now with the graces of the New Covenant afforded to us. If a leader in the synagogue refused to curse these Jews, they themselves could have been expelled from the Synagogue. With the malediction or curse added to the Amidah, the Christian Jew who refused to "pray" this anti-Jewish curse, would in effect have been "outed" and rejected and quite possibly killed.
The fact that the Birkat HaMinim ("prayer" number 12) was added to the Amidah close to this time in history, may possibly be indirect evidence that if not Gamaliel himself, at least others were suspected of being secret Christian Jews by the rabbis among the Synagogue.
What other reasons might we consider Rabbi Gamaliel's Christianity?