Other Biblical and Theological Considerations
In addition to one’s interpretation of the Great Commission, there are a number of other biblical and theological considerations that have a bearing on the legitimacy of the HUP as a missionary strategy.
God’s Plan for Diversity and the Tower of Babel
Proponents of the HUP argue that ethnic and cultural diversity has been a part of God’s plan for mankind from the beginning. Wagner maintains that the scattering of humanity into different language groups at Babel should not be understood merely as God’s punishment for building a tower unto heaven without taking him into account, but as God’s means for forcefully redirecting humanity toward his original intention of linguistic and cultural diversity. Other interpreters, however, disagree with this interpretation, focusing on the dispersion of humanity into different linguistic groups as a negative consequence of their sin. 
Homogeneity and the Old Testament
It is clear that throughout the bulk of the Old Testament, cultural homogeneity on the part of God’s people is generally regarded as a good thing. Israel is repeatedly commanded to keep themselves pure from the pagan customs of the people surrounding them. Glimmers of cultural diversity as a positive characteristic of the people of God are usually only hinted at through the lens of prophecy looking forward to a future dispensation. With only a few isolated exceptions, any reference to Gentiles becoming a part of the people of God was by way of assimilating, as proselytes, into the Jewish culture and way of life.
Homogeneity and the Ministry of Jesus
In the New Testament, Jesus’ earthly ministry, while directed mainly toward the “lost sheep of Israel” (Matt 10:5–7; 15:24), serves, in many respects, as a transitional bridge to the new dispensation in which there was to be no distinction between Jew and Greek, slave and free, or male and female (Gal 3:28). There are, nevertheless, some poignant moments in Jesus’ earthly ministry that point toward the impending future soon to be incarnated in the Church which impinge upon the theological discussion with regard to the HUP. “Jesus declared, ‘Is it not written, “My house shall be called a house of prayer for all the nations?”’ (Mark 11:17). The author of Mark understood that the last four words of that quote from Isaiah—for all the nations—summed up what caused the religious leaders to fear Jesus and look for a way to kill him (11:18).” 
Homogeneity and the New Testament Church
It is primarily with regard to the emergence of the New Testament Church, however, that the discussion on the theological basis of the HUP must be centered. Indeed, the ecclesiological vision articulated by Paul makes clear that the Church is to be regarded as a “new humanity,” a third category of people that is neither completely Jewish or Gentile. Yoder elucidates:
It is not the case that Judaism as a whole has accepted Christianity nor that Gentilism as a whole has accepted Christianity, even in one place. To think of ethnic units existing and acting ‘as a whole’ is pre-gospel. The gospel divides them. Some Jews believe, but many do not. Some Gentiles believe though many do not. Together those who believe form the new humankind (Eph 2:15). What has happened is the creation of a new socio-history which is neither Jew nor Greek, or is both Jew and Greek (you can say it either way as Paul does). The reality is so new that the words Paul uses for it are new creation (not only in II Corinthians but also in Galatians) and new humanity. In none of these usages (new creation, new humanity) is the new thing Paul is talking about an individual. But neither is he talking about an existing ethnic group. He is talking about a new group which is so much like an ethnic group that it can be called a nation or a people, but whose constitutive definition is that it is made up of both kinds or many kinds of people. 
If Yoder’s understanding is correct (and evidently, at least on the points covered in the preceding quote, it is), it will be helpful to think through how this spiritual reality was expressed in practical ways in the New Testament Church.
It is significant, and quite likely instructive, to note that on the Day of Pentecost the initial setting in which the Holy Spirit was poured out and the Church was born was a multicultural, multilingual one. While it appears the initial diversity of the group at Jerusalem was relatively limited in scope, consisting of ethnic Jews and Gentile proselytes, even a cursory reading of the book of Acts makes clear that the cultural diversity of the universal Church was meant to extend far beyond these initial parameters. Though it is not possible to know the ethnic, cultural, and social makeup of the membership of each local church, there is ample evidence to suggest that this diversity was generally manifested on a local as well as a global basis.
Early on, in the Jerusalem church, conflicts arose that largely centered on cultural and linguistic differences. The solution, however, was not to form separate congregations, but to work toward a consensus in which the interests of all were taken into account (Acts 6:1–7). When Cornelius and his family came to faith, nothing is said of forming a Gentile church in Caesarea (Acts 10, 11:1–18). Antioch was apparently a multicultural church with a multicultural leadership team (Acts 13:1). Paul worked with a multicultural traveling apostolic band (Acts 20:4).
Yet Paul adapted his evangelistic approach when preaching to different cultural groups. He preached in synagogues to both Jews and God-fearing Gentiles (Acts 13:5, 14–16, 26; 14:1; 17:1–4, 10–12, 17; 18:4–5, 19; 19:8). In Ephesus, in the Hall of Tyrannus, he conducted his work in such a way that both Jews and Greeks heard the gospel (Acts 19:10; 20:21). When rejected by the Jews, he specifically turned to the Gentiles (Acts 13:46; 18:6; 19:9). He contextualized his message to a particular people group segment when he preached at Mars Hill.
Padilla, however, emphasizes the fact that Jews and Greeks were generally evangelized together, not separately.  He also takes the implications of this assumption one step further:
It would be ridiculous to suggest that Jews and Gentiles heard the gospel together in the synagogues, but then those who believed were instructed to separate into segregated house churches for the sake of the expansion of the gospel. Such a procedure would have been an open denial of apostolic teaching concerning the unity of the church. It would have also meant that the door of the church was made narrower than the door of the synagogue, where Jews and Gentiles could worship together. The suggestion is so farfetched that it can hardly be taken seriously. 
Wagner, however, dares to make just such a suggestion.  And he is willing to stake his defense of the HUP upon his assertion: “What were the precise sociological lines along which church growth actually took place under Jesus and the apostles? The validity of the homogeneous unit principle may stand or fall on the answer to that question.” 
In order to support his presuppositions, Wagner resorts to speculation: “Thus, while local congregations in Antioch were very likely established within particular homogeneous units, the leadership of the church as a whole included representatives of several different racial and regional groups, all of whom probably came from outside Antioch itself.”  Various commentators have concluded, however, that from the evidence available, it is far more likely that New Testament congregations tended to be at least as culturally and socially diverse as the local setting in which they were found. 
An important milestone in the development of cultural diversity within the fledgling Christian movement was the Jerusalem Council (Acts 15). While a logical option for the apostles and elders gathered to give voice to their collective opinion regarding the incorporation of Gentiles into the up-to-that-point primarily Jewish Christian movement may well have been to suggest the segregation of Gentile and Jewish believers into separate congregations, it does not appear that was an option that was ever even considered. 
One of the most powerful examples of the significance of ethnic integration found in the history of the New Testament Church is the encounter between Paul and Peter (or “Cephas”) narrated by Paul in Galatians 2:11–14. It is especially noteworthy that when Paul “opposed him to his face,” it was because he and Barnabas “were not acting in line with the truth of the gospel.” Schnabel explains:
Paul insists that Peter and Barnabas and the other Jewish believers in the church in Antioch must continue to fellowship and worship in the same church as Gentile Christians do, which includes eating meals together. In other words, Paul expects the Jewish believers—whether veteran leaders such as Peter or new Jewish converts—to belong to the same local congregation as the Gentile Christians do. 
It is quite clear that for Paul the matter of racial and ethnic reconciliation was not an advanced level elective in the school of Christian discipleship, but rather, part of the core curriculum.
Homogeneity and Paul’s Theology of Reconciliation
Several passages in which Paul explains his theology of reconciliation help to confirm this assertion. Ephesians 2:11–21, analyzing the effects of the blood of Christ with regard to the separation between Jews and Gentiles, states that through his crucifixion, Christ “has made the two groups one and has destroyed the barrier, the dividing wall of hostility,” and speaks of them as forming “one body” composed of “fellow citizens” and “members of his household.” Romans 3:22, 1 Corinthians 10:32, 1 Corinthians 12:13, 2 Corinthians 5:16–21, Galatians 3:28, and Colossians 3:11 all emphasize the gospel significance of the eradication of differences between Jews and Gentiles. Schnabel, a leading evangelical authority on the theology and missionary ministry of Paul, concludes: “Paul’s emphasis on the unity of a local congregation in which Jews, proselytes, God-fearers and Greek and Romans who have come to faith in Jesus Christ live and learn and worship together proceeds from the foundational significance of the missionary message he preaches.”  In spite of all this evidence, however, Wagner makes the incredible claim that “to the end of his career [Paul] taught that people need not cross racial, linguistic, or class barriers in order to become Christians. He was the first-century champion of the homogeneous unit principle.” 
Homogeneity and Revelation
A final biblical passage that has a bearing on the question of the HUP is the celestial vision of Revelation 7:9–10 of “a great multitude . . . from every nation, tribe, people and language, standing before the throne and before the Lamb,” and worshiping God. Independent of the view one takes regarding the more controversial aspects of biblical eschatology, it appears clear that this vision corresponds to that of “the church of the firstborn, whose names are written in heaven” referenced in Hebrews 12:22–24, which serves as the model for present-day earthly expressions of the eternal, universal Church, as manifested in local congregations. Though ethnic, social, and linguistic differences are still recognizable, redeemed representatives of each “homogeneous unit” come together as one in order to lift a harmonious chorus of praise to the Lamb who by his blood has reconciled them to God and to each other.
 Harvie M. Conn, “Looking For a Method: Backgrounds and Suggestions,” in Exploring Church Growth (ed. Wilbert R. Shenk; Grand Rapids: Eerdmans, 1983), 90–91.
 DeYoung et al., United by Faith, 19.
 Yoder, “The Social Shape of the Gospel,” 282–83. On this point, see also Manuel Ortiz, One New People (Downer’s Grove, Ill.: InterVarsity Press, 1996), 130; Costas, The Church and Its Mission: A Shattering Critique from the Third World, 128; Bosch, “The Structure of Mission: An Exposition of Matthew 28:16-20,” 239–40; Padilla, “The Unity of the Church and the Homogeneous Unit Principle,” 287.
 Padilla, “The Unity of the Church and the Homogeneous Unit Principle,” 295.
 Ibid., 296.
 “The context in which Paul writes . . . however, was not one of mixtures of Hebrews and Hellenists, Jews and Greeks, Egyptians and Parthians in the same local house churches. Rather, the Christian churches of the first century, as we have seen, did develop along homogeneous unit lines just as they have for nineteen centuries afterward.” Wagner, Our Kind of People, 129.
 Ibid., 109.
 Ibid., 125.
 See, for example, Padilla, “The Unity of the Church and the Homogeneous Unit Principle,” 300; Eckhard J. Schnabel, Paul the Missionary (Downer’s Grove, Ill.: IVP Academic, 2008), 408. Wayne McClintock, “Sociological Critique of the Homogeneous Unit Principle,” International Review of Mission 77, no. 305 (January 1988): 108. Frederick W. Norris, “Strategy for Mission in the New Testament,” in Exploring Church Growth (ed. Wilbert R. Shenk; Grand Rapids: Eerdmans, 1983), 271; DeYoung et al., United by Faith, 30.
 Padilla, “The Unity of the Church and the Homogeneous Unit Principle,” 294–95.
 Schnabel, Paul the Missionary, 407.
 Ibid., 406. See also 408, 412.
 Wagner, Our Kind of People, 136.