b. “Through the eternal Spirit.” Some translations render the word spirit with a capital letter, and others use a lower-case letter. In the original Greek all the letters were written uniformly, so that we cannot determine whether the author of Hebrews meant one or the other.
What can we learn from the theological context of this passage? What do the Scriptures say? Again, we cannot be certain as to the exact intention of the author as we view the rest of Scripture. The four Gospels say nothing about the Holy Spirit’s role in the suffering of Christ. On the other hand, when Jesus preached in his hometown synagogue at Nazareth, he read from the prophecy of Isaiah, “The Spirit of the Lord is on me” (Luke 4:18; Isa. 61:1; and see Isa. 42:1). Says Donald Guthrie, “The statement in Hebrews is a logical deduction from the gospel portrait of Jesus.” Even though we would have been more certain if the author had written “Holy Spirit” instead of “eternal Spirit,” we know that Jesus was indeed led by the Holy Spirit. For example, Luke writes: “Jesus, full of the Holy Spirit, returned from the Jordan and was led by the Spirit in the desert, where for forty days he was tempted by the devil” (Luke 4:1–2).
Kistemaker, S. J., & Hendriksen, W. (1953–2001). Exposition of Hebrews (Vol. 15, pp. 251–252). Grand Rapids: Baker Book House.