Who are the Ephesians in The Bible?
"...in thee shall all the families of the earth be blessed." (Gen.12:3)
That is... all the Gentile nations outside of Abraham's lineage might be "adopted" into God's Family of the Faithful.
The early Gentile churches [called-out-ones] of God; Ephesus, Corinth, etc., following Jesus' ascension into heaven, the sending of the Holy Spirit, and the advent of Paul were the beginnings of the fulfillment of the above promise to Abraham of the salvation of mankind, through "faith in Jesus Christ" -- the "Seed" of Abraham.
"The Promises were spoken to Abraham and to his seed. The Scripture does not say 'and to seeds,' meaning many people, but 'and to your Seed,' meaning one person, who is Christ." Gal.3:16 NIV)
"The Scripture foresaw that God would justify the Gentiles by Faith, and announced the gospel [good news] in advance to Abraham: 'All nations will be blessed through you.' So those who have faith are blessed along with Abraham, the man of Faith." (Gal.3:8-9 NIV)
The Ephesians were simply "Faithful people" who lived in and around the region of Ephesus and became, through Paul's subsequent instruction and guidance, part of God's predestined whose Faith would spread to other "called-out-ones" of God down through the centuries... on, until Jesus returns with His Kingdom.
"...To the saints in Ephesus, the Faithful in Christ Jesus... for He chose us in Him before the creation of the world to be Holy and Blameless in His sight. In Love He predestined us to be adopted as His Sons through Jesus Christ, in accordance with His Pleasure and Will..." (Eph.1:1-5 NIV).
The Ephesians were among the first of God's core group of believers, whose Faith in Christ would increase and spread and grow and be passed on to the next generation of God's church, until the Day that Jesus returns.
And Paul's "letter of instruction" to the Ephesians is included as part of God's Word for the instruction and edification of the end time generations of His church.
"In Him we were also chosen, having been predestined according to the plan of Him who works out everything in conformity with the purpose of His Will, in order that we, who were the first to Hope in Christ, might be for the Praise of His Glory. And you also were included in Christ when you heard the Word of Truth, the gospel of your salvation. Having believed, you were marked in Him with a Seal, the promised Holy Spirit..." (verses 11-13).
The Ephesians were a part of the humble beginnings of the "church" [called-out-ones] that Christ said He would build.
"...on this Rock I will build My church [of whom the Ephesians were one "branch" of the Vine - John 15:1]..." (Matt.16:18 NIV).
"...for they drank from the Spiritual Rock that accompanied them, and that Rock was Christ." (I Cor.10:4 NIV)