In this post, I'll talk a little about Jacob Milgrom's "Excursus 34: The 'Ger'" in his Jewish Publication Society commentary on Numbers.
The ger was a Gentile resident alien in the land of Israel. In discussing where they came from, Milgrom refers to the strangers who "attached themselves to Israel during their flight from Egypt (Exod. 12:38, 48; Num. 11:14) as well as Canaanites who attached themselves to Israel after the Conquest (Joshua 9:3ff.) (page 398). Whether or not Milgrom believes in the historicity of the Exodus and the Conquest, I do not know. Milgrom may be saying what he thinks was the historical origin of the gerim, or he may be talking about how the biblical text accounts for them.
An item of interest to me is the laws of the Torah that the gerim had to observe. This is of relevance to me because of my religious background in Armstrongism, which said that non-Jews had to observe the law of Moses---such as the Sabbath, the holy days, the dietary laws, etc. A while back, I read a lengthy article by Ronald Dart that was responding to a Church of God (Seventh Day) booklet. The Church of God (Seventh Day) booklet argued that Christians do not have to observe the annual holy days, for those were the national days of Israel.
Armstrongites had responded to this sort of argument in a variety of ways: by saying that people in the United States and Britain were Israel and thus had to observe the holy days, by arguing that the church is spiritual Israel and is thus obligated to observe God's law for Israel, and by contending that God's law is for everyone---Jew and Gentile---since the law is what points out our sin, and we certainly wouldn't say that only Jews can sin, right? But Ron Dart made a point that I had not encountered before: that Gentiles in the Torah kept the annual holy days, for the Torah affirms that there shall be one law for the Israelite, and for the stranger (or ger).
Milgrom's excursus is about what laws the Torah mandates for the gerim to keep. His argument is that the gerim had to observe the prohibitive commandments---the "Thou shalt nots", whereas they did not have to keep the positive commandments---unless they wanted to do so. That means that they couldn't murder, steal, commit sexual sins, and sacrifice their kids to Molech, but also that they did not have to offer sacrifices. If they wanted to sacrifice, then there were rules about how they were to do so, but they did not have to offer them. Regarding the annual holy days, how this played out was as follows: the gerim did not have to keep the Passover, unless they wanted to do so, in which case they'd have to be circumcised. But they were forbidden to eat leaven during the Days of Unleavened Bread or to work on the Day of Atonement.
But what about the passages of the Torah that say there shall be one law for the Israelite and the stranger? Doesn't that indicate that even Gentile gerim were under all of the Torah, just like the Israelites? Milgrom states that those sorts of passages apply "only to the case given in the context; it is not to be taken as a generalization" (page 399). And there are indications in the Torah that the gerim did not have to observe all of the laws that the Israelites did. Deuteronomy 14:21 says that the Israelites cannot eat an animal that dies of itself, but they can give it to the ger. And Milgrom also argues on the basis of Leviticus 3:17 and 7:25 that gerim, unlike the Israelites, could eat the suet, and Milgrom's rationale is that the gerim did not have to offer sacrifices, so they could eat the suet, whereas the Israelites had to offer the suet of their sacrificial animals on the altar (Leviticus 7:25).
Of course, I cannot generalize with the word "Torah", for there are different laws on the animal that dies of itself. Leviticus 7:24-25 prohibits the eating of such an animal, and it threatens that those who do eat it will be cut off. Leviticus 17:15 states that anyone who eats such an animal---Israelite and ger---has to wash. And Deuteronomy 14:21 bans it for the Israelites, but not for the ger.
That brings me to other points. First of all, the rationale of P was that neither the Israelite nor the ger was allowed to defile the land. In this view, certain acts defile the land, regardless of who does them, and so gerim were prohibited to do those acts. But, second, the command in Leviticus 17:15 that gerim must wash raises questions in my mind. The general principle is that gerim had to observe negative commandments, but not positive commandments. But is not the command to wash a positive commandment? And what about sin offerings? Did gerim have to offer those, or could they simply leave their sins unatoned? A similar situation occurs in Numbers 19:10, where God commands the Israelites and the gerim to purify themselves of corpse contamination with the ashes of a red heifer. Isn't that a positive command? And yet, Milgrom states in his note that the gerim had to purify themselves so that they wouldn't defile the land. Again, certain acts defile, regardless of who does them, and so even a ger who commits a defiling act needs to rectify the situation.
Back to the topic of the holy days, do Deuteronomy 14:29 and 16:11, 14 require gerim to attend the festivals? My hunch is "no." Gerim probably wanted to attend them because they desired to eat and to be merry, but I doubt that they were required to do so. But, if they did attend, the Israelites had to share their food with them, and the gerim were to rejoice.
Some of you may find this post useful. Personally, I'd like more information about what laws the Israelites had to observe that the gerim did not: was it just the Passover, the ban on eating an animal that died of itself, and the ban on eating suet (if you accept Milgrom's argument on this), or was there something else? I've read commentators who say that the laws for the Gentiles in Acts 15 were based on the commands for the gerim in the Torah: in both cases, Gentiles had to observe some laws, but not others. But gerim could not work on the Sabbath or the Day of Atonement, nor could they eat leavening on the Days of Unleavened Bread. A number of Christians like to point to Acts 15 to claim that Gentiles are exempt from those sorts of laws. But, if Acts 15 is modeled after the Torah's laws on the ger, does that claim fall flat?