Psalm 23:5 You prepare a table before me...
[OP]: Just what does this table represent?
First, except in the most qualified sense, this is not what is in mind in Psalm 23:5 -

The word "table"
The Hebrew term for "table" is שֻׁלְחָן šulḥān (71× in the Hebrew Bible), still the common word in use in Israeli Hebrew. But in the world of the psalmist, it isn't certain whether this is a "slab top supported by three or more legs" piece of furniture. As the BDB definition makes clear, a šulḥān could be also be some kind of mat.
It is important also to note the distribution in the Hebrew Bible of this simple lexeme. It appears frequently as one of the temple accoutrements (e.g., Exodus 25:23; 37:10; 40:22; Num 4:7; etc.). Here, with the dimensions given and instructions for its transportation and use, it resonates with a "table" in the modern connotation (slab-top-on-legs furnishing). It is, then, a sacred item for use in tabernacle (and later temple, 1 Kings 7:48; cf. Ezekiel 41:22).
The other frequent context for this term is the "table" of a king, governor, or high official (e.g. Judges 1:7; 1 Samuel 20:29; 2 Samuel 9:7; 1 Kings 4:27; 10:5; Nehemiah 5:17): the place where courtiers, retainers, and guests ate from the king's (or official's) bounty.
Very occasionally, a šulḥān is found in private use, but this is rare (e.g. 1 Kings 13:20; 2 Kings 4:10). Possibly Proverbs 9:2 belongs here too, but this chapter's depiction of rival feasts looks much more like the "high status" situation, analogous to that of the royal or official court.
When we are confronted with a "prepared table" in Psalm 23:5, then (cf. Isaiah 21:5), we need to think of something like a religious or royal setting: something a cut above the ordinary, in any case.
"Table" in context
This brings us to the verse in question. As many commentators note, this is clearly hospitality language, in which the LORD is the "host", and the psalmist the "guest". With the preceding discussion of šulḥān in mind, it is clear that the "host" at "table" is likely to be a person of considerable status, and the setting that of the royal (or sacred) court most likely.
This makes even more sense of the "presence of enemies", as this is not a neutral feast, but rather a display of provision and largesse in which the host's favour for the guest is seen all the more sharply for having the "enemies" excluded and looking on. It is provision that implies protection.1
Kenneth Bailey develops the hinterground of the "hospitality" theme.2 He goes on to make the suggestion that since food preparation was traditionally women's work in the ancient Near East (and beyond, one might add), this incorporates a "female component" to God's character in the psalm. This might be slightly over-interpreting, but worth pondering all the same.
Summary
The "table" of Psalm 23:5 is a place of royal provision in which the Deity's generosity for the psalmist is depicted. It thus extends the sense of divine care experienced by the psalmist by adding another metaphorical layer to the pastoral (23:1-3) and pilgrimage (23:4) metaphors which precede.
Notes
- This is the insight of Andrew E. Arterbury and William H. Bellinger, Jr., "'Returning' to the Hospitality of the Lord A Reconsideration of Psalm 23,5-6", Biblica 86.3 (2005): 387-395 [or at JSTOR].
- K. Bailey, The Good Shepherd: A Thousand-year Journey from Psalm 23 to the New Testament (SPCK, 2015), see esp. pp. 54-57.