The word psyche is used throughout the New Testament and, due to its range of meanings, is translated with a variety of English words like "soul," "life," "heart" or "mind." And yet, as Hart points out, when we use a variety of English word to translate a single Greek word readers miss the fact that the same Greek word is operating across all these various instances. This obscures how categories of New Testament thought are a bit different from modern categories.
For example, if you translate the word psyche as "mind" or "soul" it can trick the modern reader into making a distinction between the material and the spiritual, between the psychological and the supernatural. Modern people make a hard metaphysical distinction between having a "mind" versus having a "soul." But this is an distinction foreign to the New Testament. In short, by alternatively translating a word like psyche as either "mind" or "soul" modern translations allow readers to superimpose their metaphysical assumptions onto the New Testament, obscuring just how differently the New Testament conceived reality. The Bible becomes metaphysically comfortable to us, conforming to our assumptions, rather than strange and startling.
Again, Hart seeks to highlight and draw attention to these differences in his translation. In the case of psyche, the overriding meaning of the word is akin to "life," "life force," or "life giving principle." The Greek word psyche is similar to the Latin word anima. As Hart points out, psyche was considered to be part and parcel of physical existence. Where we make a hard distinction between the material (body) and the spiritual (soul) components of human beings, the ancients saw more of a unity. The psyche was the force of material, animal, animate life. Consequently, the "soul" (psyche) was as mortally contingent as the body.
Which brings us to the word pneuma, translated as "spirit."
As used by the New Testament authors, pneuma points to life and power outside of the material realm. Thus, where modern readers might read "soul" and "spirit" as synonymous, the New Testament makes a distinction. Specifically, where modern readers would tend to group "soul" with "spirit," the New Testament would group "soul" more with "body." Schematically:
Modern Metaphysics: Soul/Spirit vs Body
New Testament Metaphysics: Body/Soul vs Spirit
You see this at work in Hart's translation in the way he highlights how psyche and pneuma are set up as contrasting adjectives in some Pauline passages, which makes for some very unusual translations. For example, here is 1 Corinthians 15.44-47, Paul contrasting our mortal bodies with the resurrection body:
It is sown a psychical body, it is raised a spiritual body. If there is a psychical body, there is also a spiritual. So it has also been written, "The first man Adam came to be a living soul," and the last Adam a life-making spirit. But not the spiritual first, but rather the psychical, the spiritual thereafter. The first man out of the earth--earthly; the second man out of heaven.
Yes, this is a weird, jarring translation. But Hart's translation does capture how psyche is being contrasted with pneuma, a contrast between a "soulish" or "physically animated" body versus a body that, in the resurrection, will be constituted from something more durable and lasting--a spiritual, heavenly, pneumatic body.
Here's another instance of Paul using this contrast from 1 Corinthians 2.14-16:
But a Psychical man does not receive the things of God's Spirit; for to him it is folly, and he is unable to know them, since they are discerned spiritually. The Spiritual man, moreover, discerns all things, yet is discerned by no one. "For who has known the mind of the Lord, who will give him instruction?" And we have the mind of the Anointed.
Yes, "Psychical man" is really weird, but that's the virtue of Hart's commitment to strangeness. For example, consider how modern translations render ĻĻ ĻĪ¹Īŗį½øĻ Ī“į½² į¼Ī½ĪøĻĻĻĪæĻ (psychikos de anthropos) in this text: "natural man" (NIV), "those who are unspiritual" (NRSV), "the natural person" (ESV).
Only Hart's very straightforward translation of psychikos de anthropos as "psychical man" alerts the reader to the fact that the Greek word psyche is in play here, the word that is often translated as "soul." You'd never know, reading modern translations, that the word often translated as "soul" is associated with things like "natural" and "unspiritual" as it is in this text.
However, if we appreciate the point above, that in the New Testament imagination the "soul" was the life force of the body, we can see Paul's contrast and point. A "soulish" or "psychical" person is just a normal, natural, animate person--the human animal. The "spiritual" or "pneumatic" person, by contrast, has been infused with a power that comes from beyond the physical and psychical realm.
And if this pneumatic infusion is hard to wrap your head around, think about the Transfiguration of Jesus.