NOTES for Eph 4:5
Paul's words about one Lord, one faith and one ablution ("baptism") call back a certain early symbol of faith, which in the early Christian Churches, basing on what we know today, was many. It is not surprising: because in those days the observation of commandments was for the Church more important than the unity of the opinions on whatever theological questions. And all the same, sometimes appeared before the Church even in those days, the necessity to formulate a common opinion on the most important, fundamental questions, connected above all with the relation to the personality of Jesus Christ. The expression "one Lord, one faith, one baptism " becomes on the lips of the apostle a concentrated expression of this relation. By "Lord" we doubtless understand the Savior Himself, Who in the time of His earthly ministry didn’t refuse this title.
As seen, in this case it is about His recognition as the King of this Kingdom, which He brought into the world. For Paul such recognition is very important: because the messianic conceptions in the Judaism of that period were few, and the Christian conceptions couldn’t be attributed to the traditional conceptions. They were also far enough from mass popular representations of the Messiah, and before all, exactly in the understanding of what the messianic Kingdom is, and how it is. The indication of the Messiah, as King of the Kingdom, about which spoke Jesus, in such a situation became a kind of identification mark, according to which one could distinguish the followers of Jesus from the representatives of a multitude of the other messianic movements.
Faith in such a Messiah and in such Kingdom really became the foundation of the spiritual life of every Christian: because it is in particular the inhabitant of this Kingdom that Jesus wanted to see. As seen, the symbol of faith was necessary for the first Christians not only and not so much in order to separate theirs from the foreigners by some external signs, but in order not to get lost on the spiritual way leading to the Kingdom.