This verse at the outset seems extremely problematic, for it appears to be teaching the preexistence of a soul - a soul that can be good or bad and "enters" a body that is more or less "defiled" based on its degree of goodness. Though most New Agers are not well enough versed in the Sacred Scriptures to pick up on this verse from the Book of Wisdom, some philosophers and modernist exegetes have pointed to this verse as supporting the notion that many of the Jews of the Old Testament believed in reincarnation, and that this belief is actually Scriptural.
Of course, Eastern beliefs in reincarnation were quite foreign to Judaism - there was only one group in the sphere of the ancient Mediterranean and Middle Eastern world which held to the belief, and that was the Platonists.
Plato had advocated the hypothesis that each soul, upon death, is reincarnated in another body. Some souls are reborn immediately after drinking from the "River of Forgetfulness" (Lethe) while others who were especially wicked had to undergo a period of purifcatory torment in a purgatory-like state before being reborn. Like in Hinduism, the degree of happiness enjoyed in the next life by the reborn soul was related to how good or wicked it had been in the previous life. Platos' full theory of reincarnation is developed philosophically in the dialogue Phaedo and is stated in mythic terms in book 10 of the Republic, in the section commonly called 'The Myth of Er' (click here for text).
Was there any Platonic influence on the writer of the Book of Wisdom? Back in the days when it was becoming fashionable to attribute all of the Sacred Scriptures to the influence of other religions, some did make the case that Wisdom, especially Wisdom 8, is directly influenced by Platonic thought.
Without going into the exegetical details, most scholars today, even liberal ones, reject any Platonic origins for these verses, pointing out that the Book of Wisdom teaches the futility of trying to know the truth from the created world apart from the special wisdom that comes from God (see Wis. 9:6); the author is writing Wisdom against a pagan philosophical world-view that believed in the capability of reason to know the absolute truth without divine illumination. Platonic philosophy was the epitome of the thought that Wisdom is written to refute and it is highly unlikely that the author would have made use of a Platonic argument in an effort to disprove pagan philosophy.
Furthermore, even if Wisdom 8:19-20 may seem to imply a preexistent soul, it does not give any indication that this soul once existed in another body - that is, if it did imply the soul's preexistence (which I don't concede), it would be more in the Origenist sense in which the souls of individuals are created and exist before they are incarnated in bodies but have no prior carnal life. At the most we could argue that Wisdom 8 supports the preexistence of the soul but it definitely does not assert reincarnation.
So what is the best way to understand these verses? Is the soul preexistent? Of course the answer to that is a resounding 'no.' Let's look at the verses one more time:
As a child I was by nature well endowed,
and a good soul fell to my lot;
or rather, being good, I entered an undefiled body (Wis. 8:19-20)
First we need to see that the author is not taking us back to some time before birth, but is talking about his upbringing - "as a child." The first verse simply states that the author was born with a good disposition: a good intellect, healthy curiosity about the world and a desire to do good.
When we come to the second line, "a good soul fell to my lot," we have to understand that when the Old Testament speaks of a "soul" it is not in the same manner that we today are accustomed to using the phrase. As the catechism points out, the term soul usually refers to the heart of man, or the seat of his personhood, meaning the place where he makes decisions and ultimately chooses for or against God (CCC 363-366). So when the Scriptures say a "good soul fell to my lot" the author is not making a metaphysical statement about how he received his particular "soul"; rather, he is simply repeating what is said in the previous verse (a literary technique called Hebrew parallelism) in stating that as a child he had a naturally good disposition. It is common human experience that some children are naturally disposed to have a certain personality - some kids are quiet and introverted, some not so much so. The author merely states that he was born and raised with a good disposition and good character.
But the real tricky part comes in verse 20, where the author attempts to clarify his statement by saying "or rather, being good, I entered an undefiled body." Setting aside issues of translation and different versions of the Scriptures (some say the better translation would be "I entered a body undefiled", making the adjective "undefiled" to modify the soul that entered the body, not the body itself), we could still argue that this does not support the preexistence of the soul.
The main reason for this is that it would contradict what the author says only a few chapters later, in Wisdom 15, where it is said of the wicked man:
...he failed to know the one who formed him and inspired him with an active soul and breathed into him a living spirit (Wis 15:11).
Here the traditional understanding of all souls as coming from God as their source is affirmed, using the Genesis language of God "breathing" souls into men an animating them out of His own unique creative act that is new for each individual. It would be very difficult to reconcile Wisdom 8 with Wisdom 15 (and Genesis 1 for that matter) if we were meant to read Wisdom 8 in a New Age sense.
We should not be overly literal when reading passages about a soul or spirit "entering" man, as in Wisdom 8 and 15. We know that these are metaphors the Scriptures use to describe how God vivifies the body by the infusion of the soul, something nobody really understands. It can be truly said that at the moment of conception, a soul created immediately by God "enters" the embryo to bring about new life. Language about souls "entering" bodies needs to be read in light of the narrative of the creation of man in Genesis and not in any Hindu or New Age context foreign to the culture of the time.
The reason this language about a soul "entering" a body sounds odd is simply because the subject of the sentence is the soul where usually we speak about the soul as the object or direct object. For example, "God breathed into Adam a living soul," versus "the soul of Adam entered him." Both sentences say the same thing but have different emphases. Saying "the soul of Adam entered him" does not imply a preexistence inasmuch as we understand it to be saying the same thing as "God breathed into Adam a living soul," and both are metaphors for a creative process that is shrouded in the depth of the veil of divine mystery.
The only remaining question is this issue of the soul entering an "undefiled body" - this seems to indicate that the body, at the time of birth or creation, can already be in certain states of purity or defilement, and that this is somehow related to the goodness of the soul that goes into it.
Again, we must not read our own philosophical context onto what the passage is saying. Nothing in this passage henceforth has made any mention of preexisting souls, but simply of God-given natural dispositions; it is in this light that we must look at the verse. This cannot be any reference to Platonism at any rate, because according to Plato, the body itself is a defilement. The idea of a soul possibly entering an undefiled body would not be a Platonic thought at all - according to Plato, even the souls of the righteous are weighted down by a carnal form that is the source of all defilement. Wisdom 8:20 is certainly not Platonic in any sense, nor should it be read in anything other thanh an ancient Jewish context. If we temper this passage with what we know from our Lord's words, that it is what proceeds from the heart that defiles a man, not what goes in to the body (Matt, 15:11), we can easily interpret this passage in consonance with the rest of the Scriptures.
First, while the body itself, strictly speaking, cannot be a source of "defilement", we know that the degree to which a person's fleshly or bodily life is or is not sinful depends on the condition of the soul, as our Lord teaches and as even Plato acknowledges (an unjust soul leads to unjust actions). A man with an upright and virtuous soul will live his bodily life in an austere and temperate manner, while a person with an intemperate soul will be more prone to sins such as gluttony, lust and avarice. The quality of the soul determines the quality of the life. This is a fundamental spiritual truth and this is what Wisdom 8:19-20 is teaching. Wisdom 8:20 simply means that because the author had a good and temperate disposition, he was not prone to sins which defile the body. This is simply our Lord's teaching in Matthew 15, put in an Old Testament context in which ritual defilement and impurity was still very important.
At any rate, there is much more that can be said about this, but I think this suffices.