(For a short introduction to Philo, his family and their connections with Rome, see Philo, On the Embassy to Gaius 8-10.)

The treatise On the Special Laws is part of Philo’s Exposition of the Law, a series containing “a treatise on the creation, three extant Lives of biblical patriarchs, four books on Mosaic law, and two concluding treatises on virtues and rewards and punishments,” which Maren Niehoff considers as having been composed after Philo’s embassy to Rome (Niehoff, Philo of Alexandria, p. 7-8). On the Special Laws is divided into four books that contain a detailed interpretation of the laws of the Pentateuch, sorted in accordance with their relationship to the ten commandments of the Decalogue, which Philo sees not merely as laws but also as general categories. In the section from which the passage under study is taken, Philo deals with the prescriptions related to the first commandment, which he understands to be Exodus 20:3 (“You shall have no other gods before me”), and interprets as the condemnation of polytheism and the obligation to recognize the One and truly existing God (Daniel, De Specialibus Legibus, p. xiv-xv).
It is in this context that Philo mentions the obligation for Israelites to welcome proselytes and treat them well. Although born in a polytheistic environment, proselytes have freed themselves from false beliefs and representations and have loved the truth enough to “cross over” to piety (eusebeia) and the Jewish commonwealth or people (politeia, understood here as the community of the citizens; see Philo, On Virtues 106-108; Carlier, La cité de Moïse, p. 129-171). Philo uses several verbs that convey the idea of departure and movement from one place to another, such as metaballō (§51), methormizō (§51), apoleipō (§52), automoleō (§52), and of course proserchomai (§51), with which the word prosēlytos is connected etymologically. Philo’s description of the spiritual and social journey of the proselytes has a parallel in On Virtues 102, where he writes: “Besides setting down laws regarding fellow nationals (homoethneis), he maintains that proselytes (epēlytai) are to be considered worthy of every privilege, since, having forsaken their family by blood, their homeland, their customs, the temples and images of their gods and the gifts and honors offered to them, they have traveled to a fine new home, from mythical fabrications to the certainty of truth and the veneration of the One and truly existing God” (translation by Walter Wilson, Philo of Alexandria: On Virtues, p. 64). In both treatises, Philo describes conversion as a switch from “mythical fabrications” (mythika plasmata) to the truth, as well as a radical departure from one’s original environment, an estrangement from one’s kin, friends, and fellow citizens. This description recalls the story of Abraham in Genesis 12:1-5 (in Virt. 279, Philo actually presents Abraham as a model for proselytes).
Philo’s description of proselytes also displays striking convergences with the way Tacitus depicts converts to Judaism in the Histories, composed at the beginning of the second century CE. Tacitus writes: “Those who are converted to their ways follow the same practice [circumcision], and the earliest lesson they receive is to despise the gods, to disown their country (exuere patriam), and to regard their parents, children, and brothers as of little account” (Histories 5.5.2; trans. Clifford H. Moore, LCL, 183). The Roman historian expresses a strong aversion to some of the Jewish customs and sees the conversion of a Roman citizen to Judaism as a betrayal of quintessential Roman values, namely pietas (piety, which means the scrupulous observance of one’s duties toward the gods, but also toward one’s parents, the emperor, etc.) and fides (loyalty). By contrast, Philo praises those who have left behind these duties and relationships for the sake of piety toward the God of Israel, and new kinship ties. Both authors describe the same phenomenon but from opposite viewpoints.
The spiritual kinship that Philo mentions in relation to proselytes is in his eyes the true kinship, which ranks higher than natural family relationships (Berthelot, “L’humanité de l’autre homme”, p. 139-148). Another passage of On the Special Laws (I.317) illustrates this point particularly well. It is still part of Philo’s discussion of the first commandment, but this time Philo deals with the issue of false prophecy, and comments on Deuteronomy 13:2-6, which commands the Israelites to put to death a false prophet who tries to entice Israel to worship foreign gods. The members of his family are obligated to kill him too, which leads Philo to assert: “But as for these kinships, as we call them, which have come down from our ancestors and are based on blood-relationship, or those derived from intermarriage or other similar causes, let them all be cast aside if they do not seek earnestly the same goal, namely, the honour of God, which is the indissoluble bond of all the affection which makes us one. For those who are so minded will receive in exchange kinships of greater dignity and sanctity” (Spec. I.317, translation by F. H. Colson, LCL, p. 283; see further Berthelot, “L’humanité de l’autre homme”, p. 144-147; Carlier, La cité de Moïse, p. 309-311). As in Spec. I.52, Philo uses the expression “indissoluble bond” (desmos alytos) to describe the relationship established between those who worship God. Philo opposes biological kinships (or “blood-relationships,” aph’ haimatos syngeneiai) to “more holy and sacred kinships” (semnoterai kai hieroprepesterai syngeneiai). Elsewhere he also uses the expression “higher kinship” (anōtatō syngeneia) to refer to the latter, and defines it as “one civic community (politeia), (with) the same law (nomos), and one God” (Spec. IV.159, my translation). The higher or spiritual kinship is equivalent to membership in the community that is rooted in shared laws and the cult of the One and truly existing God (for this designation of God, see Virt. 102). Therefore proselytes can participate in this kinship irrespective of their non-Israelite genealogy and their idolatrous ancestors.
By contrast with On Virtues 102-104, which refers to the commandment to love the ger/ prosēlytos as oneself (Leviticus 19:34), in On the Special Laws I.51-53 Philo does not quote a biblical verse in particular. The way he describes how proselytes are to be integrated to Israel is characterized not by biblical references but by Greco-Roman notions: isotimia (§51), isonomia and isoteleia (§53) (according to Josephus, Augustus restored isonomia and isoteleia to the Jews living in Greek cities in Cyrenaica [A.J. XVI.160-161]). Because Philo conceives of the Jewish people as a politeia, a civic body, he views the proselytes as having joined this politeia and thus as having received a Jewish “citizenship”. The fact that Philo emphasizes the equality of the new citizens and those who are native-born before the law (isonomia, isoteleia) indicates that he tends to define the Mosaic politeia as a “structure of integration” rather than a “structure of participation,” to use Philippe Gauthier’s terminology (Gauthier, “La citoyenneté en Grèce et à Rome”). Gauthier characterizes Greek poleis as structures of participation, and Rome as a structure of integration (he emphasizes that Hellenistic poleis continued to function as structures of participation until at least the beginning of the first century CE; “La citoyenneté en Grèce et à Rome”, p. 172-173). To put it succinctly, the main issue in a Greek context was the functions fulfilled by the citizen, rather than his personal status. By contrast, for most Roman citizens, especially from the end of the Republic onward, participation in political assemblies in Rome had little significance. The crucial element constituting Roman citizenship was rather one’s personal status as a subject of Roman law, with a corresponding set of rights and obligations (Marotta, La cittadinanza romana, 31; Ando, Imperial Ideology, Chapter Nine). Even though Philo was familiar with Greek philosophical thought on political regimes, his conception of the Mosaic politeia and the integration of new “citizens” reflects both the emphasis put on Torah and Covenant in the definition of membership in the people of Israel (the Exodus paradigm) and the Roman model of citizenship, the central aspect of which was one’s status as a subject of law (Berthelot, “Judaism as ‘Citizenship,’” 123-125).
Philo concludes this section on proselytes by a warning that seems based on Exodus 22:27 LXX, “You shall not curse gods (theous)”. The Hebrew text has Elohim, which is a plural but is understood as a singular, referring to God (“You shall not curse God”). The Greek translators, however, chose to translate in the plural. Jewish authors writing in Greek therefore understood the verse to forbid offensive words against the gods of the nations (see further Philo, Questions and Answers on Exodus II.5; On the Life of Moses II.205; Josephus, Jewish Antiquities IV.207; Against Apion II.237). Philo again emphasizes that proselytes have rejected the wrong beliefs (literally “folly” or “vanity,” typhos) of their parents and ancestors. Yet the understanding that they were wrong should not lead proselytes (or Israelites) to blaspheme against the gods that other men revere, lest the latter speak in the same way about the God of Israel. This passing remark points to Philo’s concrete awareness of the problems and tensions that conversion to Judaism could raise for Jewish communities living among Greeks, Romans or polytheists more broadly.