In chapter 8 of All That the Prophets Have Declared, Martin Foord grapples with both the general question of how the Old Testament is appropriated in the New, and the specific question of how Paul is using Psalm 68 in Ephesians 4 – given that he appears to change it from ‘receiving gifts’ to ‘giving gifts.’ Here’s my summary from the conclusion of the book:
Martin Foord argues that Paul respects the context of the Psalmic text that he cites in Ephesians 4, but feels at liberty to reinterpret the text’s meaning in the light of the subsequent revelation of the Christ event. Some might respond that this ‘reinterpretation’ involves unacceptable change (from ‘receiving’ to ‘giving’ gifts); but the acceptability or otherwise of Paul’s reinterpretation depends upon one’s assessment of whether the subsequent triggering revelation was in fact from the same divine author. It is certainly Paul’s assumption that this is the case. In this regard, Foord proposes the motif of the revealed ‘mystery’ as a key to Paul’s use of the Old Testament: what God had formerly disclosed as a ‘mystery’, he has now brought to plain fulfilment in Christ. This validates the revisiting and reconsidering of the earlier revelation, in which the content of the gospel had been cloaked in mystery.