In this passage, Paul cites Deuteronomy 25:4, which deals with the treatment of oxen, and asks, “Is it for oxen that God is concerned?” Paul then asks, “ἤ δι’ ἡμᾶς πάντως λέγει,” which he then affirms. If the first question is read rhetorically as expecting a negative, and if the second question is translated, “Does he not speak entirely for our sake?” then it seems that Paul is denying the original intent of the Law. This is the way Origen understood this text (On First Principles, 4.2.6).
But the second question could be translated as, “Surely he says this for us, doesn’t he?” (NIV). BDAG lists five senses (with glosses) for πάντως: (1) “pert[aining] to strong assumption, by all means, certainly, probably, doubtless,” (2) “pert[aining] to thoroughness in extent, totally, altogether,” (3) “expression of inevitable conclusion in view of data provided, of course,” (4) “expression of lowest possible estimate on a scale of extent, at least,” (5) “with a negating marker . . . not at all . . . by no means.” BDAG lists 1 Corinthians 9:9 under sense one, and this coheres with the translation of the NIV (see also Fee, NICNT [1st ed.], 408; Thiselton, NIGTC, 686; Garland, BECNT, 410).
This non-exclusive translation of πάντως means that the first question need not be understood to absolutely exclude God’s concern for oxen. When the second question is understood as the NIV translates it, Paul is not denying relevance to oxen; he is simply saying there is an extended application to humans as well.
The Old Testament context points toward this extended application. In its context, the command regarding oxen stands alone among commands to provide for the needy. The command regarding the oxen was, in context, an illustration of the kind of care that people should have for one another. This means that Paul interpreted Deuteronomy 25:4 with more care to its original context than those who claim he succumbed to allegory.
Godet makes this point well.
Does not this whole context [in Deuteronomy] show clearly enough what was the object of the prohibition quoted here? It was not from solicitude for oxen that God made this prohibition; there were other ways of providing for the nourishment of these animals. By calling on the Israelites to exercise gentleness and gratitude, even toward a poor animal, it is clear that God desired to inculcate on them, with stronger reason, the same way of acting toward the human workmen whose help they engaged in their labour.
F. Godet, Commentary on St. Paul’s First Epistle to the Corinthians, trans. A. Cusin (Edinburgh: T. & T. Clark, 1893), 2:11. (See also Ciampa and Rosner, CNTUOT, 719; Merrill, Deuteronomy, NAC, 325).