This post is part of an ongoing series on Paul and Pneuma, Justin and Judaism.
Scholars have long noted that Paul and Justin differ on who possess Abraham as ancestor and who belongs to true Israel. Less satisfactory, however, have been explanations as to why Paul and Justin diverge over these claims. It is my contention that these differing interpretations arose because of Paul’s Stoic worldview and cosmology and Justin’s Middle Platonic view of the world and the cosmos. That is, Justin’s largely Platonic worldview in some sense prevented him from sufficiently understanding Paul’s largely Stoic conceptions—especially concerning pneuma—and its influence on the boundaries of the Christian community. This section considers Paul’s and Justin’s conceptions of pneuma and how their cosmologies caused them to understand the Abrahamic ancestry and identity of Israel differently.
To understand the differences between Paul’s pneumatology and Justin, one must enter the world of ancient philosophy. The Stoic development of Platonic physics which was popular in Paul’s day held that everything that “is” (including the soul and virtues) is a material body (σῶμα) or a property of body. Our post-Cartesian minds should not interpret this materiality as purely mechanical or (negatively) materialist, but rather as natural materiality, a corporeality in which reality is physically real. According to Chrysippus, the animating force of reality was pneuma, a mixture of air and fire which permeates the whole cosmos and serves as a self-moving vehicle of divine reason. In Stoic cosmology, the pneuma functioned as the universal controlling entity through a peculiar double movement (κινησις πνευματικη) in which it simultaneously moved into itself and out of itself. Pneuma was often associated with the divine as the seminal principle of the world, indicating that God—like everything else in the Stoic cosmos—was made of pneumatic matter.
Stoic cosmology proves particularly important because a number of New Testament scholars have argued that Paul inhabited a Stoic worldview, at least when it came to his conception of the pneuma. For example, in Romans 8:14-17 Paul speaks of pneuma as the binding agent which unites Gentiles to Christ—the pneuma of God confirms (συμμαρτυρεῖ) that human pneuma now belongs to the divine. Likewise in Galatians 4:1-7, the Gentiles join Christ by taking his pneuma into their hearts (εἰς τὰς καρδίας), that is, by mixing their substances with his. This pneumatological connectivity forms new kinship, kinship that is not “spiritual” in the Cartesian sense of the term, but “material” in the Stoic sense. In practicality, for Paul this meant that Gentiles who were brought into Christ received the pneuma of Christ—real participation in the material stuff of Christ—through baptism into Christ. Furthermore, it is not just faith that brings one into contact with divine pneuma, but the pneuma of Christ through faith (Gal. 3:26) provides subsistence within the family of God. As Thiessen summarizes, “Paul consistently portrays the reception of the pneuma in ways that coincide closely with Stoic conceptions of both pneuma and krasis…. The presence of the pneuma means that believers share the very substance of Christ and therefore share the shape of his life, death, and resurrection….” Thus the Gentiles—who previously did not belong to the family of God—were pneumatically grafted into the People of God through faith. The key here is not just that the Gentiles-in-Christ now belong to the God, but also that the status of the Jews has not changed. That is, while Christ has pneumatologically opened up God’s kinship group to the nations, that group remains primarily composed of God’s “first family”—the Jews (Rom. 9:4-5; Phil. 3:4b-6).
 Christoph Jedan, Stoic Virtues: Chrysippus and the Religious Character of Ethics (London: Continuum, 2009), 11. Walter C. Wright, “The Source of Paul’s Concept of Pneuma,” The Covenant Quarterly 41 (1983): 20. Aeschylus, The Suppliant Maidens (trans. Richmond Lattimore, Chicago: University of Chicago Press, 1953-56), 66-7. Jedan locates Stoicism at the junction of three intellectual schools: traditional polytheistic Greek religion, ancient philosophy-theology, and a materialist ontology. Michelle Lee offers a helpful discussion of the three forms of the Stoic body: different, adjacent, and unified. See Michelle Lee, Paul, the Stoics, and the Body of Christ (Cambridge: CUP, 2006), 49-50.
 Jedan, 9-10. Terrence Paige, “Who Believes in ‘Spirit’? Πνευμα in Pagan Usage and Implications for the Gentile Christian Mission,” HTR 95 (2002): 425.
 Jedan, 14-5, Stanley K. Stowers, “What Is ‘Pauline Participation in Christ’?” in Redefining First-Century Jewish and Christian Identities: Essays in Honor of Ed Parish Sanders (ed. F.E. Udoh et al, Notre Dame, I.N.: University of Notre Dame Press, 2008), 355.
 Jedan, 15. Cicero, On the Nature ofthe Gods 11.7.19.
 Jedan, 14. Diogenes Laertius, Lives 7.136. Paige, 425.
 N.T. Wright, Paul and the Faithfulness of God (Minneapolis: Fortress, 2013), 232. Stanley Stowers, “What Is ‘Pauline Participation in Christ’?,” 355. Stanley Stowers, “Paul and the Terrain of Philosophy,” Early Christianity 6 (2015): 156. Thiessen, 114. Troels Engberg-Pedersen, “Paul’s Body: A Response to Barclay and Levison,” JSNT 33.4 (2011): 438-9.
 Johnson Hodge, 75-6. Thiessen writes that, “To receive the pneuma is to be enclothed in Christ because the pneuma is the pneuma of God’s son, who is Christ (Gal 2:20; 4:6; cf. Rom 8:9; Phil 1:19).” See Thiessen, 111.
 Thiessen, 117, 126. Rom. 6.3-11; Gal. 3.27.
 Thiessen, 105-6. Gal. 3.26-9. For a differing position, see Stephen Westerholm, “The Judaism Paul Left Behind Him” in The Making of Christianity: Conflicts, Contacts, and Constructions: Essays in Honor of Bengt Holmberg (ed. M. Zetterholm and S. Byrskog, Winona Lake, I.N.: Eisenbrauns, 2012), 356.
 Thiessen, 114.