Here is my overly literal translation of Rom 8:17 -
Now, if children, also heirs, heirs indeed of God, co-heirs now of
Christ, if indeed we co-suffer with, so that also we may be
co-glorified with.
Note all the "co-" verbs here, characterized in the Greek by sun/sum prefix on these Greek verbs. Now, in English, these are awkward, and a "smoother" translation would read something like this:
Now, if children, also heirs, heirs indeed of god, joint-heirs of
Christ, if indeed we suffer with [Him/Christ], so that we may be
glorified with [Him/Christ].
Thus, Paul emphasizes Christ's complete identification with humanity in various ways. See appendix below. This whole concept of being "joint heirs" or "co-heirs" is part of the NT metaphor of adoption and Jesus being our brother.
The idea of sinners being adopted as Sons of God occurs infrequently in the NT and only by Paul (Rom 8:15, 23, 9:4, Gal 4:5, Eph 1:5). However, Jesus appears to unmistakably allude to adoption in John 3:1-8 and 1:12, 13 where we are able to become children of God; Rom 1:7, 2 Cor 1:2, Eph 1:2, 5, Gal 1:3, 4:5, Phil 1:2, 4:20, Col 1:2, 1 Thess 3:11, 2 Thess 1:1, 2, 2:16, 1 Tim 1:2, etc. This is in contradistinction to the Jewish leaders whom Jesus accused of having the Devil as their father, John 8:44.
Thus, adoption is spoken of in the present and future tenses:
- Adoption in our current life is a metaphor of the reception of the spirit, “the spirit of adoption” (Rom 8:15) signifying a complete change of attitude and way of life which frees us from the constraints of the law, slavery to sin and fear of spiritual poverty, with the added bonus of the promise of future glory in heaven. This process is technically (theologically) called “conversion”, which see.
- Adoption in the future life (Rom 8:23) is used as a metaphor of glorification when the saints are translated to heaven.
Adoption is used as a figure of the privileges of sinners under the protection of God in the Christian life, but Gal 4:5 links the idea to redemption and hence to atonement. Thus, it is more a symbol of the change of life from sinner and assurance of heaven (that is conversion) than of only atonement. The latter (psychologically) creates the former. That is, a person of royalty is free from fear of slavery and poverty, but must be generous to those in need.
Indeed, God is frequently spoken of as the “Father” of the Israelites throughout the OT, Deut 32:6, Ps 89:26, Isa 63:8-10, 16, 64:8, Mal 1:6. In the NT writers frequently refer to God as “the Father”, Gal 1:1, Eph 1:3, 5:20, 6:23, Phil 2:11, 1 Thess 1:1, 1 Cor 15:25, 2 Cor 1:3, 11:31, James 1:27, 1 Peter 1:2, 3, 2 Peter 1:17, 2 John 3, etc; or “My Father”, Matt 11:27, 12:50, 18:35, 20:23, 26:53, Luke 10:22, 15:58, John 5:17, 8:19, 54, 10:17, 18, 29, 14:21, 23, 15:18, etc. The Lord’s Prayer begins with “Our Father”, Matt 6:9, see also Gal 1:4, 1 Thess 3:11, 2 Thess 2:16, Titus 1:4, Col 1:3, Phil 1:2, 4:20, etc.
The metaphor of adoption is used as a proxy for the promises of the covenant in Rom 9:4, Eph 1:5, Gal 3:26-29, 4:5; this is apt as the covenant and adoption grant great privileges.
The metaphor of adoption is extended by the New Testament’s repeated idea of Christ being our brother (Heb 2:11-13, 17, Ps 22:22, Isa 8:17, 18, Matt 12:48, 49, John 20:17, Rom 8:29) following adoption.
APPENDIX - The Imitation of Christ
Here are further ways we are like Christ according to the NT:
- Partakers of the divine nature. 2 Peter 1:4
- Because Jesus was persecuted, so are His followers. John 15:20, 21.
- Be kind because God is kind. Luke 6:34, 35
- Be servants to others as Jesus was. John 13:15-17, 1 Peter 4:11b, Matt 20:24-28.
- Be patient as Jesus was patient. 1 Tim 1:16.
- We are to have the mind of Christ. Phil 2:5, 1 Cor 2:16
- Jesus is the light of the world (John 1:4, 9, 8:12, 9:5) and so are we (Matt 5:14-16, Phil 2:14)
- Jesus is the “firstborn” Luke 2:7, Rom 8:29, Col 1:15, 18, Heb 1:6, Rev 1:5, and we are to compose the church/assembly of the firstborn, Heb 12:23; see also Rom 8:23 & Rev 14:4 where we are also called first-fruits to God and the Lamb.
- Jesus is our sacrifice of atonement and likened to a sacrificial lamb offered for us John 1:29, 1 Cor 5:7, Eph 5:2, 1 John 2:2, 4:10, Heb 10:10, 12, Rom 3:25, 1 Peter 1:19, etc. Similarly, the life of a Christian is lived sacrificially for Christ Rom 12:1, Phil 2:17, Heb 13:15.
- Jesus, by His sacrifice on the cross, reconciled sinners to God (Rom 5:10, Col 2:16, 1:20, 22, 2 Cor 5:19), and we must also be involved in the “ministry of reconciliation” (2 Cor 5:18, 19) as “ambassadors for Christ” (2 Cor 5:20).
- Jesus died to sin and was raised to a new life, never to die again. This is also the process of every sinner in Jesus will also die to sin (at baptism) and be raised to a new eternal life, free of sin. See Rom 6:8-11.
- Jesus is our great high priest (Heb 4:14, 15, 7:26-28), so too, we are a holy nation of priests. 1 Peter 2:9.
- Jesus is the chief corner-stone and we are also stones in the building. 1 Peter 2:4-6.
- Jesus is the chief shepherd, and elders are to shepherd the flock as He would. 1 Peter 5:1-4.
- We are to be conduits of Jesus’ “water of life”. John 4:13, 14.
- The Levitical Laws are almost all set in the context of “I am the LORD”, essentially saying that, “This is who I am, do likewise”. See Lev 18 and 19 among many others.
- Jesus is the promised “seed” (Gen 13:15, 24:7) of Abraham (Gal 3:16) and so are we (Gal 3:29, Rom 9:8).
- After His ascension, Jesus was seated at the right hand of the Father in heaven (Ps 110:1, 5, Luke 22:69, Matt 26:64, Acts 2:33, 7:56, Rom 8:34, Eph 1:20, Col 3:1, Heb 1:3, 10:12, 12:2, 1 Peter 3:22), and so will we (Rev 3:21, see also Eph 2:6).
- Jesus is “THE Son of the Most High” (Luke 1:32, Mark 5:7, 8:28) and Christians are called “sons of the Most High” (Luke 6:35).
- Jesus was sent by God to preach and live the Gospel (John 1:33, 4:34, 5:24, 36, 36, 38, 39, 44, 6:57, 7:28, 33, 8:16, 18, 42, 9:4, 12:44, 45, 49, 14:24, 15:21, 16:5, 20:21) and we are sent to preach the Gospel (Matt 28:19, 20, John 20:21, Gal 1:1).