„Is Paul saying that the rock trailed behind the wandering Jews?”
Well, yes. In what sense?
First of all, we have to take into account that God is often referred to as a Rock, in the OT. For instance:
He is the Rock, his works are perfect, and all his ways are just. A faithful God who does no wrong, upright and just is he.
And you will sing as on the night you celebrate a holy festival; your
hearts will rejoice as when people playing pipes go up to the mountain
of the Lord, to the Rock of Israel. (NIV)
There are many more examples, a concordance would bring them out easily.
On the other hand, some commentators (see E. E. Ellis, “A Note on First Corinthians 10:4”, in Journal of Biblical Literature, 76/1957, pp. 53–56) noticed that Paul is taking here a targumic style and is alluding a Jewish legend according to which that rock followed the Israelites during their wanderings in the desert:
T. Sukka 3.11
So the well, which was with Israel in the wilderness [...] travelling
with them up the mountains and going down with them in the valleys
(From Sukkah, Mishna and Tosefta, tr. A. W. Greenup, Translations
of Early Documents, Series III: Rabbinic Texts, SPCK, London, 1925,
What is important to see, I think, is that Paul is using here a Jewish legend as a framework for transfering to Christ the title, ‘the Rock’, used in the Jewish tradition for Yahweh. Through this he is inferring that Christ is God.
From a different outlook, there are other commentators (I take as an example J. F. Walvoord, R. B. Zuck, The Bible knowledge commentary : An exposition of the scriptures (2:526), Victor Books, Wheaton, IL, 1983-1985) who noticed that in the OT the drinking of water from the rock is mentioned twice:
I will stand there before you by the rock at Horeb. Strike the rock,
and water will come out of it for the people to drink." So Moses did
this in the sight of the elders of Israel. (NIV)
Then Moses raised his arm and struck the rock twice with his staff.
Water gushed out, and the community and their livestock drank.
Now it is truth that these two verses can talk about one single event, yet according to Walvoord & Zuck (see above), Exodus 17:6 is marking the beginning of Israel’s wilderness wanderings in the desert, whereas the event from Numbers 20:11 is happening near the ending of wanderings. Now if Paul is referring to both of these events, this would be the reason why he is saying that Christ, in whom he is seeing the source of supernatural water, accompanied/followed/trailed them: it was with them from the beginning until the end of the wanderings. Therefore God was with them everywhere. Therefore God is omnipresent. So, as we discover in Walvoord & Zuck, another possible answer would be that in 1 Corinthians 10:4, Paul is talking about the omnipresence of God. Later on, in Jewish and Christian theological contexts, omnipresence was discussed as an attribute of God. I am well aware this can take a bit to far. It would be intersting to see if Paul is using anywhere else a notion related to "omnipresence". However I think it is interesting to see it unfolding in the following centuries (found it in Walvoord&Zuck and in various other commentaries).
Is Paul talking here about Christ as „Rock” (metaphor for God in the OT)? Is Paul talking about Christ as “omnipresent” (attribute of God)? Or is he just willing to express that Christ is God?
Now let's return to the original question:
"... was the rock literally Christ in a different form?"
Most likely not. In fact the text is not very complex here:
1 Corinthians 10:4
... they drank from the spiritual rock that accompanied them,
and that rock [the spiritual one] was Christ. (NIV)
The auhtor is saying that the rock was "spiritual". If you bear with me a little word play, we could say perhaps that from a spiritual point of view, the spiritual rock was literally Christ.
"Or is he calling attention to its value as a metaphor for Christ?"
If the above is correct, then the answer to this goes to: "Most likely yes." And if this is true, then really we have to think that in the ANE a metaphor is not just a figure of speach or a clever way to express things. When Paul is writing, Saussure is still to come. In the ANE, when a metaphor is used in a religious text, the meaning is most likely a theological one.
To conclude: my opinion, based on 1 Corinthians 10:4 and on later commentaries, would be that the rock was not literally Christ, but the rock was spiritually Christ. And that Paul, using a figure of speach, is calling attention to Christ as God, using a syllogism in a Jewish context:
- the Jewish context is:
Isaiah 30:29 (and other OT verses alike) + Exodus 17:6 + Numbers 20:11 + the legend from T. Sukka 3.11
- the syllogism is:
A. God/he is the rock (of Israel) >
B. God is faithful (as a rock) and accompanies Israel all the way through the desert >
C. that rock was Christ >
D. therefore Christ is God. ///