Messianic psalms

i) The current kerfuffle regarding the reorganization of the OT dept. at WTS has reignited debate over the sense in which the OT "points" to Jesus. Take the so-called messianic psalms. Ps 22 is traditionally classified as a messianic psalm, but Ps 23 is not. Is just a subset of the 150 psalms messianic. If so, what criterion distinguishes messianic psalms from non-messianic psalms? Or is there a sense in which the whole Psalter is messianic? 

And, of course, this question extends to the OT generally. Does the OT contain messianic types and prophecies? Or is the entire OT messianic? If so, how so?

ii) From a Christian standpoint, we can mount a pretty simple and direct argument that Ps 23 is about Jesus. If Jesus is God, and God is a shepherd, then Jesus is David's divine shepherd. 

iii) The sense in which the whole OT is messianic is not that every sentence, person, place, or event is a cipher for Jesus. Rather, it turns on the overall function or purpose of the OT. If the primary purpose of the OT is to document man's hopeless condition, and his desperate need for salvation, then that necessity points to a Savior. In that functional or teleological sense, the whole OT is messianic. That's how the OT is fulfilled. 

iv) You also have scholars like Alec Motyer, Desi Alexander, and John Sailhamer who mount the argument from prophecy, not based so much on individual oracles, but messianic motifs. An evolving expectation. Or certain categories, viz. the new Adam, new David, divine warrior, promised seed, suffering servant. 

v) Now let's revisit (i). I suspect the reason that only some of the psalms are traditionally classified as messianic presumes the relation between the messianic prophecy and the argument from prophecy. The argument from prophecy is predicated on the premise that "the prophets foretold events whose occurrence could not have been humanly foreseen" (C. S. Evans).

Therein lies its evidential value. A prediction whose fulfillment could not be humanly foreseen or humanly arranged. This supplies independent evidence for the claim. Separable from prior belief in Jesus. 

Ps 22 is traditionally classified as messianic because it seems to be predictive. It's hard to read without seeing how uncannily it corresponds to the Crucifixion. The specificity is arresting. Of course, some people challenge that, but my immediate point is not to defend it but to state the rationale.

By contrast, Ps 23 doesn't seem to be predictive or evidential. If you already believe that Jesus is Yahweh, then you can infer that this is about Jesus. But by itself, the Ps 23 doesn't give you any independent reason to believe it points to Jesus. It's not a messianic in that sense. It might be messianic, but not predictive–as defined by the argument from prophecy. 

Should we classify messianic psalms as messianic prophecies? If so, then it's harder to classify the entire Psalter as messianic. Perhaps, though, that classification system is unduly influenced by the argument from prophecy–where the fulfillment has autonomous evidentiary value. Something you can appreciate apart from what you already believe about Jesus. 

The argument from prophecy is biblical, and important to Christian apologetics. But should it control how we classify OT messianism?