Paul, an apostle of Jesus Christ by the will of God, to the saints which are at Ephesus, and to the faithful in Christ Jesus:
By, х dia (G1223)] - 'through the will of God:' called to the apostleship through that same "will" which originated the Church (Ephesians 1:5; Ephesians 1:9; Ephesians 1:11: cf. Galatians 1:4): a cause of thanksgiving to God's grace on his part, and calling for recognition of his authority on theirs.
Which are at Ephesus - see 'Introduction.'
To the saints ... and to the faithful - the same persons: Greek, 'to those who are saints, and faithful in Christ Jesus.' The sanctification by God is put before man's faith. God's grace in the first instance sanctifies us (i:e., sets us apart in His eternal purposes as holy unto Himself); and our faith, by God's gift, lays hold of salvation (2 Thessalonians 2:13; 1 Peter 1:2). Consecration to God is the idea prominent in "saints."
In Christ - in living union with Christ.