The amazing point to be made is that the “one” is to take place in this world of “things” where individual beings appear to be “united” accidentally. What's being affirmed is that the union of "persons" is not accidental. What seems to be suggested is that we work within a new epistemological horizon whereby we are able to perceive the personal as divine “in” the world, rather than outside it, above it or after it.
Let’s consider the scriptural foundation and the Ratzinger-Benedict commentaries.
1) a) “I pray… for those also who through their word are to believe in me, that all may be one, even as thou Father, in me and I in thee; that they also may be one in us, that the world may believe that thou hast sent me. And the glory that thou hast given, I have given to them, that they may be one, even as we are one: I in them and thou in me; that they may be perfected in unity, and that the world may know that thou hast sent me, and that thou hast loved them even as thou hast loved me" (Jn. 17, 20-23).
b) Galatians: 2, 20: “I live; no, not I; Christ lives in me.”
3, 16: “The promises were made to Abraham and to his offspring. He does
not say, ‘And to his offsprings,’ as of many; but as of one, ‘And to they offspring,’ who is Christ.”
3, 28: “For all you who have been baptized into Christ have put on Christ.
There is neither Jew nor Greek; there is neither slave nor freeman; there is neither male nor female. For you are all one in Christ Jesus. And if you are Christ’s, then you are the offspring of Abraham, heirs according to promise.”
2) The “One” is not the accidental binding of individual substances. It is the conversion of persons into the one Person of Jesus Christ where they find their irreducible uniqueness. The reason for this is the divine Person of Jesus as “prototype” of the meaning the human person. Since His Person is nothing but relation to the Father and does not stand as autonomous “substance” (in itself) before the Father but a pure “for” the Father, the human person approaches “being” Him, who is prototype, in the measure that he/she goes out of self in love and service to others.
Conversion: “A Death Event”
The operative word for becoming Christ is “conversion.” The “Sequela Christi” (“Following Christ”) has to be understood in these terms. “Following Christ is not an outward imitation, since it touches man at the very depths of his being. Being a follower of Christ means becoming conformed to him who became a servant even to giving himself on the Cross (cf. Phil. 2, 5-8). Christ dwells by faith in the heart of the believer (cf. Eph. 3, 17), and thus the disciple is conformed to the Lord. This is the effect of grace, of the active presence of the Holy Spirit in us.”
John Paul punctuates the point with St. Augustine’s: “Let us rejoice and give thanks, for we have become not only Christians, but Christ (…). Marvel and rejoice: we have become Christ!”
Ratzinger comments: “To explain … that becoming and being a Christian rest upon conversion would still be much too weak a way of putting things. This is not to deny that such an interpretation is aiming in the right direction, but the point is that conversion in the Pauline sense is something much more radical than, say, the revision of a few opinions and attitudes. It is a death-event. In other words, it is an exchange of the old subject for another. The `I’ ceases to be an autonomous subject standing in itself. It is snatched away from itself and fitted into a new subject. The `I’ is not simply submerged, but it must really release its grip on itself in order then to receive itself anew in and together with a greater `I.’”
An Outstanding Eye-Opening Observation and Hermeneutic of Paul’s 1 Cor. 12, 12 of Ratzinger:
Text: 1 Corinthians 12, 12: “As in an organism there are many members working in harmony, so it is with Christ.”
Exegesis: “Paul does not say `as in an organism there are many members working in harmony, so too in the Church,’ as if he were proposing a purely sociological model of the Church, but at the very moment when he leaves behind the ancient simile, he shifts the idea to an entirely different level. He affirms, in fact, that, just as there is one body but many members, `so it is with Christ…’ The term of the comparison is not the church, since, according to Paul the Church is in no wise a separate subject endowed with its own subsistence. The new subject is much rather `Christ’ himself, and the Church is nothing but the space of this new unitary subject, which is, therefore, much more than mere social interaction. It is an application of the same Christological singular found in the Letter to the Galatians. Here, too, it has a sacramental reference, though this time it points to the Eucharist, whose essence Paul defines two chapters before in the bold assertion: `Because there is one bread, we who are many are one body’ (10, 17)… soma [the Greek word for “body’], may be translated as `one subject’…”
 John Paul II, “Veritatis Splendor,” #21.
 Ibid. Augustine’s commentary “In Johannis Evangelium Tractatus,” 41, 10: CCL 36, 363.
 J. Ratzinger, “The Spiritual Basis and Ecclesial Identity of Theology,” in The Natuare and Mission of Theology, Ignatius (1995) 51.
 Ibid 53-54.