These words spake his parents, because they feared the Jews: for the Jews had agreed already, that if any man did confess that he was Christ, he should be put out of the synagogue. (John 9:22 KJV)
Nevertheless among the chief rulers also many believed on him; but because of the Pharisees they did not confess him, lest they should be put out of the synagogue: (John 12:42 KJV)
Meaning
Put out of the synagogue simply means ex-communication. In those days, believers in Jesus were doomed to be put out of the synagogue as their punishment.
Ripley 4 Gospels
Put out of the synagogue; be excommunicated. The Jewish ex-communication was a severe punishment. There were three degrees of it. The first excluded the person from intercourse with the people, even with his own family, for the space of thirty days; he was not allowed to approach a Jew at a distance nearer than four cubits. If he gave no signs of penitence, the time could be doubled and even trebled. The second separated the person from all sacred meetings, was accompanied with dreadful curses, and forbade all intercourse with others. The third was still severer and was regarded as a final and total exclusion of the person from the community.
Adam Clarke’s Commentary
Put out of the synagogue. That is, excommunicated-separated from all religious connection with those who worshipped God. This was the lesser kind of ex-communication among the Jews and was termed nidui. The cherem, or anathema, was not used against the followers of Christ till after the resurrection.
British Family Bible
should be put out of the synagogue. Should be placed under a sentence of ex-communication. Dr. Whitby.
The Jews had three different sorts of ex-communication. The first is that which is here meant by putting out of the synagogue, and which our Saviour expresses by “separation,” Lu 1:1-24:53; Lu 6:22. The effect of this ex-communication was to exclude men from the communion of the church and people of God, and from his service, after which no Jews would hold intercourse with them. The second sort included the first, but extended farther, to the confiscation of goods into the sacred treasury, and devoting them to God. In the third, the person was anathematized, and devoted; and, as some conceive, according to the law, Le 27:29, was to be put to death, although others think it amounted to no more than a final sentence, by which he was left to the judgment of God, to be by Him cut off from the congregation of Israel. Abp. Tillotson.
Family Bible Notes
Put out of the synagogue; excluded from the people and worship of God–excommunicated. Tyrants in church and state try by pains and penalties to prevent men from embracing the truth. They appeal not to reason and conscience, but to force. They labor to preclude inquiry, stifle private judgment, and in many cases prevent those under their control from receiving the instruction afforded by the providence and word of God.