Exodus 12:43-51 offers several stipulations regarding who may eat of the Passover and who may not. Strangers to the covenant, transients and uncircumcised non-Jews among Israel are forbidden to eat the Passover lamb.
A certain Syrian Gentile used to pretend to be a Jew and go up and partake of the Passover sacrifices in Jerusalem, boasting, "Your Torah says, 'No alien is to eat it. . . no uncircumcised person shall eat of it.' Yet I eat of the very best of the Passover lamb." Back in Babylon, Rabbi Yehudah bar Batyra asked him, "Did they let you have the fatty tail of the lamb?" "No," the Gentile replied. "Then when you next go up to Jerusalem for Passover, demand the fatty tail of the lamb from them," Rabbi Yehudah said. When the Gentile went up for the next Passover, he said to them, "Give me with the fatty tail of the lamb." The others at the Seder (Hebrew) literally, "order"; an ordered event, especially the meal eaten on Passover exclaimed, "But the fatty tail belongs to the Most High! Who told you to ask for the fatty tail?" "Rabbi Yehudah bar Batyra told me to ask for it," he answered. "What is this meaning of this?" they wondered. They investigated the man and discovered that he was Syrian and had him executed. Then they sent a message to Rabbi Yehudah bar Batyra, saying, "Peace unto you Rabbi Yehudah bar Batyra, for even though you live in Nisibis of Babylon, your net is spread in Jerusalem." (b. Pesachim 3b)
Oftentimes non-Jewish believers within the Torah movement misunderstand these laws to indicate that they are banned from keeping a Seder. Others construe that an uncircumcised person cannot keep a Seder.
To be sure, this passage and Genesis 17 would have been the two primary texts which Paul's opponents used to argue for Gentile exclusion from Israel. It would appear that the Torah is saying that unless a person is circumcised and has made a conversion to Judaism, they cannot celebrate Passover. But a careful reading of the text will demonstrate otherwise.
This is the ordinance of the pesach: no ben-necaris to eat of it; but every man's slave purchased with money, after you have circumcised him, then he may eat of it. A transient (toshav) or a hired servant shall not eat of it. But if a ger sojourns with you, and offers the pesach to the LORD, let all his males be circumcised, and then let him come near to offer it; and he shall be like a native of the land. But no uncircumcised person may eat of it. The same law shall apply to the native as to the ger who sojourns among you. (Exodus 12:43-49 with retranslation according to the Hebrew).
To begin with, several terminology issues need to be resolved. The passage above uses three different terms to describe non-Israelites.
The first word used in the passage is ben-necar, "son of a stranger."
The word neichor/nochri usually describes something alien and to be excluded. This word group is regularly used of Israel's enemies, and of the nations that are characterized by foreign gods and idolatry. The foreigner designated by these terms is usually viewed as dangerous and hostile. This word group regularly represents foreign peoples or foreign wives. The adjective is used to describe the "strange woman" of Proverbs who has betrayed her husband and family. 1
That is why Classical Judaism understands the term to mean "an apostate." An apostate or idolater is forbidden to make a Passover unless he is a slave of an Israelite and has consented to be circumcised and take on the Abrahamic faith. One can see that this reading would certainly support Paul's theological opponents who were saying that Gentiles must be circumcised.
The second word used in the passage to describe a non-Israelite is a transient (toshav). The transient is paired with a hired-wage earner and it implies someone who is only temporarily passing through the community of Israel. 2 The transient is contrasted with the ger, a non-Israelite who lives among the community. 3 The ger is subject to the same Torah as the native-born Israelite and is regarded within the people of Israel. The ger enjoys all the same rights and privileges of native born Israelites as well as the same responsibilities. The Torah stipulates that if the ger wants to make a Passover, he and his household are welcome to do so as long as they consent to circumcision.
In addition, the term translated as Passover is the pesach, a term which applies only to the Passover lamb itself, its slaughter and consumption. Thus the Torah literally does prohibit an uncircumcised person, be he Jew or non-Jew, from sacrificing a Passover lamb and from eating the Passover lamb. It is prohibited. (It is prohibited for him, but apparently not for his wife!)
This means that Paul's converts were free to remain uncircumcised, but if they wanted to make a Passover sacrifice, they would have to consent to circumcision. For most of Paul's converts, this was a non-issue. They lived far from Jerusalem. Neither they nor the Jewish community around them had access to the Temple or sacrifices. Therefore they kept the Passover, the Seder and the seven days of Unleavened Bread like the rest of diaspora Judaism - without a lamb. The only thing prohibited was the actual sacrificial lamb itself.
The Talmud, a major body of Jewish law composed between 200-500 CE. concurs. An uncircumcised non-Jew is allowed to keep the Seder and Feast of Unleavened Bread. Only regarding the actual lamb-sacrifice is he banned.
"He shall not eat of it," but he may eat unleavened bread and the bitter herbs. (Pesachim 96a quoting Exodus 12:45)
Therefore, this text would have actually been a powerful tool in Paul's hands. He would have been able to prove from this passage that the Torah allows for such a thing as an uncircumcised ger "stranger" among Israel. If that ger wanted to sacrifice a Passover lamb in the Temple and eat it, he would definitely need to be circumcised first, but not as an issue of conversion, only as an issue of sacrificial rights. Perhaps the fact that sacrifice was irrelevant to Paul's converts living in diaspora contributed to Paul's emerging theology regarding Gentile circumcision.
This means that non-Jewish and non-circumcised believers are welcome at the Seder table. They should partake of the matzah, the bitter herbs, the four cups and the whole seven day festival with a glad heart. There is no prohibition except as regards the sacrificed lamb itself, and without a Temple, there is no sacrifice. Thus Jewish and non-Jewish, circumcised and uncircumcised believers can jointly share in and rejoice in our common Passover Lamb, Yeshua The Hebrew/Aramaic name of Jesus of Nazareth. (lit, "salvation").
Notes:1. Hegg, 2003, FellowHeirs, First Fruits of Zion.