How do one get to be in Christ? Is it same as to be righteous before God? I consider Romans 8:1 as axiom.
Therefore, there is now no condemnation for those who are in Christ Jesus,
That little word in is packed with profundity, significance, and comfort for believers in Jesus Christ.
One way of approaching this little word is via one of the many names for the Church Universal: the Body of Christ. A body, of course, is composed of many parts (viz., appendages and external and internal organs), and so it is with Christ's body, the church, of which He is the Head. All of the parts of the physical body are in the body and are thus joined to the whole body. Each part has its function, but they all function together. The main point of the analogy of the body can be summed up, I feel, in the expression
"Unity within Diversity."
To be in Christ, then, is to be a part of His body.
Theologically, the word in signifies where a believer is, positionally in the eyes of God; namely, in Christ. To be in Christ is to be united with Christ in His righteousness.
"For God made Him who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him" (2 Corinthians 5:21, my emphasis).
We who are sinners saved by grace are anything but righteous. Moreover, Isaiah tells us that
"For all of us have become like one who is unclean, And all our righteous deeds are like a filthy garment; And all of us wither like a leaf, And our iniquities, like the wind, take us away" (64:6).
In other words, even the best we have to offer God cannot outweigh in the divine scale of justice our uncleanness, filthiness, and iniquities. Along comes Jesus, however, and His righteousness tips the scale in the opposite direction, so to speak.
Think of a zillion-pound weight being on one side of the teeter totter. That's our sin. Our righteous deeds piled up to the sky on the opposite side utterly fail to budge the zillion-pound weight one scintilla.
Jesus' cross death, however, means that God, when He imputes our sin to Jesus and then in turn imputes Jesus' righteousness to us when we believe, tipped the teeter totter as far as it can go in the opposite direction, as if the zillion-pound weight were but a feather! Aren't you glad you're in Christ? There is no safer place to be in all the universe, because when God sees us, He sees us in His Son. And as Paul reminds us,
"Whoever is in Christ is a new creation: the old has passed away, and all things have become new" (2 Corinthians 5:17, my emphasis).
In his article Mysticism in the Early Church, early twentieth century theologian Arthur C. McGiffert describes what Paul means by "in Christ".
The Christian man is he in whom dwells divinity. By faith, the mystical bond of union, he is brought into complete oneness with God, so that it is no longer he that lives, but the divine Christ that lives in him (cf. Gal. 3:27; 4:19; Rom. 8; Eph. 2:22; 3:17; Col. I:27 ff.; 3:3). It is a genuine physical or metaphysical unity of which Paul speaks -not simply a oneness of spirit, or disposition, or will, but of substance. Jesus Christ, who is himself divine, or the Spirit of God, who is one with Christ, enters into the believer and substitutes for his fleshly nature a spiritual and divine nature, so that he is a new creature altogether. The result of the divine indwelling is not simply union, but identity. It is not that the man and Christ are brought into intimate association, but that they become one, so that the man dies with Christ unto the flesh, and rises with him unto a new life, unto the spirit; so that what Christ does he does, and what Christ has he has.''
Consider what Paul has said earlier to the Romans.
Romans 6:3-11 (NASB) Or do you not know that all of us who have been baptized into Christ Jesus have been baptized into His death? Therefore we have been buried with Him through baptism into death, so that as Christ was raised from the dead through the glory of the Father, so we too might walk in newness of life. For if we have become united with Him in the likeness of His death, certainly we shall also be in the likeness of His resurrection, knowing this, that our old self was crucified with Him, in order that our body of sin might be done away with, so that we would no longer be slaves to sin; for he who has died is freed from sin.
Now if we have died with Christ, we believe that we shall also live with Him, knowing that Christ, having been raised from the dead, is never to die again; death no longer is master over Him. For the death that He died, He died to sin once for all; but the life that He lives, He lives to God. Even so consider yourselves to be dead to sin, but alive to God in Christ Jesus.
This inclusion in Christ is strictly by the action of God, and not of man.
1 Corinthians 1:30 (NASB) But by His doing you are in Christ Jesus, who became to us wisdom from God, and righteousness and sanctification, and redemption, so that, just as it is written, “Let him who boasts, boast in the Lord.”