In Ephesians 3, Paul shows how we know that God welcomes Gentiles, namely by “revelation.”
[You have heard of] God’s grace that was given to me for you, how the mystery was made known to me by revelation. … [The mystery of Christ] was not made known to the sons of men in other generations as it has now been revealed to His holy apostles and prophets by the Spirit (Ephesians 3:2-5).
Already, Ephesians 2:20 has emphasized the importance of “the apostles and prophets.” They, with Christ as the cornerstone, form the foundation on which God builds His one family, His one temple, His one church. In Ephesians 3, the apostles and prophets are foundational because the Spirit reveals to them God’s plan to bring all believers—Jews and Gentiles—together in “the same body” (Ephesians 3:3-6).
“Apostles” and “prophets” feature again, for a third time, in Ephesians 4. Paul begins his discussion of unity by encouraging attitudes based on seven “ones” of unity: one body, one Spirit, one hope, one Lord, one faith, one baptism, and one God and Father. He then shows how our oneness is served by Christ’s diverse gifts, that is, by the roles given for the church’s growth and unity.
[Christ] gave the apostles, the prophets, the evangelists, the shepherds and teachers, to equip the saints for the work of ministry, for building up the body of Christ, until we all attain to the unity of the faith and of the knowledge of the Son of God, to mature manhood, to the measure of the stature of the fullness of Christ (Ephesians 4:11-13).
Attain to the unity of the faith, to mature manhood.
Paul is building on the fact, already established, that the “apostles and prophets” are foundational since the Spirit has revealed His truth through them (Ephesians 2:20; 3:3-6). The other roles—“the evangelists, the shepherds and teachers”—carry that revealed truth forward. The result of this leadership is that members learn to serve, to build up Christ’s body “until we all attain to the unity of the faith,” reflecting the fullness of Jesus Himself (Ephesians 4:13). Are Christ’s teachings—also called doctrines—included in this “unity of the faith,” this “fullness of Christ”? The next section answers positively.
[We all grow into the fullness of Christ] so that we may no longer be children, tossed to and fro by the waves and carried about by every wind of doctrine, by human cunning, by craftiness in deceitful schemes. Rather, speaking the truth in love, we are to grow up in every way into Him who is the head, into Christ (Ephesians 4:14-15).
“Speaking the truth in love, we are to grow up in every way.”
In its context, then, “one faith” is more than the subjective act of believing, essential as it is to have personal faith. One faith” includes what to believe. It includes the truth, the teaching that stands firmly against shifting lies that carry away those who remain childish. Nor is “the unity of the faith” referring only to initial or elementary teachings. That unity includes matters of maturity, growing up “in every way” into the fullness of Christ (Ephesians 4:13, 15). That is the very thing Paul proceeds to do in the rest of Ephesians, revealing how Christians grow, how they should “walk” with Christ and each other. Is that growing and walking part of “one faith”? It is certainly not another faith. The “one faith” does more than teach us about forgiveness. The same saving faith continues, teaching us to grow into Christ-like maturity.