Is the Spirit of Christ in Romans 8:9 identical to the Spirit of God?
“But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of His.”
In the Greek Scriptures there is no differentiation between lowercase and uppercase letters. When the translators came across the word pneuma, they had to decide if it referred to the Holy Spirit (in which case they used “Spirit”) or not (when they wrote “spirit”). In this verse, they used capital “S” for both “Spirit of God” and “Spirit of Christ” – clearly, they believed that both referred to the Holy Spirit. I believe that they were right. In this chapter, the word “spirit” occurs far more times than in all other 15 chapters of Romans put together, and the great majority of these refer to the Holy Spirit. This verse is no exception, and it is teaching that the mark of someone who is saved is that he is indwelt by the Holy Spirit.
Why, then, does Paul make a change from “Spirit of God” to “Spirit of Christ”? Here are several suggested reasons.
First, it is vital to the argument that he will develop in the ensuing verses. Referring to the Holy Spirit as the “Spirit of Christ” (v9) enables him to state that “Christ” is “in you” (v10). He can then show (v11) that there is a parallel between how God raised Christ and how He will quicken us. “But if the Spirit of Him that raised up Jesus from the dead dwell in you, He that raised up Christ from the dead shall also quicken your mortal bodies by His Spirit that dwelleth in you.” So, by using the term “Spirit of Christ,” Paul is linking us intimately, not only with the Spirit, but also with Christ Himself, and thus paving the way to show that Christ’s resurrection is the assurance of our quickening, at His coming.
In addition, he confirms, succinctly, several glorious doctrines regarding divine Persons. First, that the “Spirit of God” is the “Spirit of Christ” shows the Deity both of the Spirit and of Christ. Second, the use of “God,” “the Spirit,” and “Christ” in such proximity is a beautiful statement of the truth of the Trinity. Third, unity in action of Father and Son is clearly implied. The two expressions remind us, for example, that the Holy Spirit was sent by both the Father (John 14:26) and the Son (John 16:7).
Moreover, “Spirit of Christ” may strike a practical note. Someone is “in the Spirit” if the “Spirit of God” dwells in him. How is he to know that the Spirit of God dwells in him? There will be evidence of Christlikeness in his life. This resemblance to Christ is produced by the Spirit, hence the designation “Spirit of Christ” is appropriate in this context.
Thus, the “Spirit of Christ” is identical with the “Spirit of God,” in that both refer to the same Person, but Paul’s use of the two phrases does indicate different characteristics of divine Persons and their work.