If not in regards to one's salvation, how do you understand one being chosen in Christ per Ephesians 1:4?
The answer is in your question. All those who are "in Christ" are chosen in time because Jesus was chosen before the foundation of the world. God did not chose who would be "in Christ" and he is certainly not the member of the Godhead who put them in Christ. The Holy Ghost put them in Christ via the new birth. No one can be in Christ before the Spirit of God began forming the body and the body of Christ cannot be formed until Jesus Christ paid the sin debt and died and rose again and ascended to heaven.
For your benefit I am going to quote the first 14 verses of Ephesians 1 and highlight the emphasized doctrine of being "in Christ." I trust you will take the time to read it.
Eph 1 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:
2 Grace be to you, and peace, from
God our Father, and from the Lord Jesus Christ.
3 Blessed be the
God and Father of our Lord Jesus Christ, who hath blessed us with all spiritual blessings in heavenly places
in Christ:
4 According as he (God the Father) hath chosen us
in him before the foundation of the world, that we should be holy and without blame before him (God the Father) in love:
5 Having predestinated us unto the adoption of children by Jesus Christ to himself (God the Father), according to the good pleasure of his (God the Father's) will,
6 To the praise of the glory of his (God the Father's) grace, wherein he (God the Father) hath made us accepted
in the beloved.
7
In whom we have redemption through his blood, the forgiveness of sins, according to the riches of his (God the Father's) grace;
8
Wherein he (God the Father) hath abounded toward us in all wisdom and prudence;
9 Having made known unto us the mystery of his (God the Father's) will, according to his good pleasure which he (God the Father) hath purposed
in himself:
10 That in the dispensation of the fulness of times he (God the Father) might gather together in one all things
in Christ, both which are in heaven, and which are on earth; even
in him:
11
In whom also we have obtained an inheritance, being predestinated according to the purpose of him (God the Father) who worketh all things after the counsel of his (God the Father's) own will:
12 That we should be to the praise of his (God the Father's) glory, who first trusted
in Christ.
13
In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation:
in whom also after that ye believed, ye were sealed with that holy Spirit of promise,
14 Which (The holy Spirit) is the earnest of our inheritance until the redemption of the purchased possession (The glorification of the body of Christ, both individually and corporately), unto the praise of his (God the Father's) glory.
The trinity is in these verses, God the Father, Christ, and the holy Spirit. God the Father is the initiator, the body of Christ is being formed on the earth from those who are believers in his death, burial, and resurrection, and the holy Spirit who seals the believer in the body as the earnest of the complete inheritance, which we know from other passages are "joint heirs" with Christ. We learn from 1 Cor 12:13 that it is the Spirit who baptizes the believer into the body and chooses his function in the body.
The purpose of God the Father is to form this body in this age in the image of Christ. What is his image. It is trinitarian, three in one and one in three. The body is a trinity, Jew, gentile, and the holy Spirit. This has been done by God before, He has put his son to death and taken the building material from his side while he slept and formed a help meet for him and woke him up and presented the person he had formed to him as his bride. He spoke as if they were the same person later.
Genesis 2:21
And the Lord God caused a deep sleep to fall upon
Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof;
22 And the rib, which the Lord God had taken from man, made he a woman, and brought her unto the man.
23 And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man.
24 Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.
This is trinitarian. Adam, Eve, the same Holy Spirit in both before the fall. Adam is the head of the woman and Christ is the head of the church.
This is the type. Read Eph 5 now.
Genesis 5:2
Male and female created he them; and blessed them, and
called their name Adam, in the day when they were created.
