There are 2 questions in the question. The one I'll address is this one:
"Is this evidence that Paul believed that being in the natural body
was like a prison?"
Setup [This is not my main point, just musings]
Paul begins his letters with his name and credentials ("Paul, an apostle of Jesus Christ"). He fills his letters with personal narrative. And he writes to gentile assemblies (though he often addresses the Jews in the communities). And his subject is God's covenant with the houses of Israel and Judah, which involves works which is uncharacteristic of Paul. Nor does it include any of his characteristic subjects such as flesh/spirit, faith without works, the body of Christ (except the verses we are considering here), etc. So there is a lot about "To the Hebrews" that argues against Pauline authorship.
However, in the last chapter there are a lot of things that suggest that Paul did write the book including the personal references and the mention in the verse at hand of "being also in the body".
Some think this is compelling evidence that Paul wrote Hebrews.
I said all that to say that I don't think Paul wrote Hebrews but the last chapter is either:
- by Paul and for some reason the letter in uncharacteristic of Paul except for the last chapter
- not by Paul but coincidentally similar to Paul's writings
- only the last chapter was written by Paul and it was appended by a redactor
- or, (and this seems compelling to me) Paul did not write any of it, but the last chapter was added with signals suggesting that it was Paul who wrote all of Hebrews
Interpretation
If Paul wrote the last chapter OR it was intended to sound as if he did then we can understand it from a Pauline perspective. In that case we can turn to one of Paul's most undisputed letters for help:
NIV 1 Corinthians 12:26 If one part suffers, every part suffers with
it; if one part is honored, every part rejoices with it.
Paul's theology can in many ways be reduced to the following premise:
NIV 1 Corinthians 12:
12Just as a body, though one, has many parts, but all its many parts
form one body, so it is with Christ. 13For we were all baptized by c
one Spirit so as to form one body—whether Jews or Gentiles, slave or
free—and we were all given the one Spirit to drink. 14Even so the body
is not made up of one part but of many.
Union with Christ is used by Paul to explain so much.
So the reasoning of the passage is Pauline even if Paul didn't write it. Paul is saying to have compassion because we are members of one another because we are members of Christ. Again, this is the Pauline thought:
NIV 1 Corinthians 12:26 If one part suffers, every part suffers with
it; if one part is honored, every part rejoices with it.
Does Paul also compare being in the body is like being in a prison? Yes, he does:
BSB Romans 7:
23 But I see another law at work in my body, warring against the law
of my mind and holding me captive to the law of sin that dwells
within me. 24 What a wretched man I am! Who will rescue me from this
body of death?
Paul compares himself to a captive prisoner of war. "Mr. Sin", the personification of sin "in his members" (his body parts) has overcome him and controls him.
So yes Paul does use a prison metaphor in his writings in Romans 7. But is that what his point is in the Hebrews passage?
I think not because then he would be saying "have compassion on those in prison because you are also in a prison - your body" which doesn't seem very compelling or Pauline. Instead I think the point is, "Believers are all one flesh so the suffering of one member is the suffering of all the members.":
ESV Ephesians 5:
28In the same way husbands should love their wives as their own
bodies. He who loves his wife loves himself. 29For no one ever hated
his own flesh, but nourishes and cherishes it, just as Christ does the
church, 30because we are members of his body. 31“Therefore a man shall
leave his father and mother and hold fast to his wife, and the two
shall become one flesh.” 32This mystery is profound, and I am saying
that it refers to Christ and the church.
I think that's more to the point.
Related:
Can we tell from the text who wrote Hebrews?
Does Hebrews 13:24 establish the provenance of the Epistle to the Hebrews?