“Since the law of Moses was abolished by the death of Christ (Colossians 2:14), and the Psalms were a part of that law, why did Paul allow the singing of psalms in Christian worship (Ephesians 5:19)?”
In the first place, when one recognizes that the Mosaic law was abolished by Christ’s death — and it certainly was (Romans 7:4; Galatians 3:24-25; Ephesians 2:14-15; Hebrews 7:12, etc.) — this fact does not mean that every truth or principle in the Old Testament suddenly became ineffective. In fact, the New Testament itself teaches otherwise.
Paul, in his letter to the saints in Rome, affirmed that the “things written aforetime,” i.e., in the Old Testament canon, “were written for our learning” (Romans 15:4). In the first Corinthian epistle the apostle taught that certain incidents in the history of the nation of Israel were provided as “our examples” (1 Corinthians 10:6), indeed they were “written for our admonition” (v. 11).
Earlier in the Corinthian correspondence, the apostle introduced an illustration from Moses’ law to buttress the proposition that gospel preachers are worthy of support. If Hebrew law provided for an ox to eat of the grain, as he trod upon it in a threshing process, then provisions most assuredly were appropriate for the minister of God’s word (1 Corinthians 9:9). The same example is appealed to in the apostle’s first letter to Timothy, in support of the idea that the elder who rules well is worthy of “double honor,” which signifies financial compensation (1 Timothy 5:17-18).
In the second place, when the scripture speaks of the abolition of the law, specific elements are in view. The law, with its bloody animal sacrifices, is not valid today as a redemptive system. The shedding of Christ’s blood nullified that. Nor is the worship ceremonialism of the old regime, with all its “carnal” features (see Hebrews 9:9-10), viable for those of this dispensation.
Finally, the term “psalm” simply means a “pious song.” It may or may not refer to one of the songs in the Old Testament book that bears that name. Many scholars believe that it is not possible to draw a hard line between “psalms, hymns, and spiritual songs” in Ephesians 5:19. One has written: “It is impossible to fix precisely the limits of these terms”; he goes on to define “psalm” as “generally a rhythmic utterance, either actually one of the O.T. psalms, or [a song] sung in their manner” (H.C.G. Moule, Studies in Ephesians, Grand Rapids: Kregel, 1977, p. 136).
But why would it not be appropriate to sing, for example, Psalm 23, as we do frequently? Is not the Savior our shepherd (John 10:11)? Or what of Psalm 8? Is it not the case that the Lord’s name is “excellent” still? Of course if a psalm was prophetic, and it has been fulfilled already, obviously it would not be appropriate to sing it as if its fulfillment was yet future.
Otherwise, there is no violation of divine law in singing a psalm, written centuries ago, that expresses the same sentiments that children of God entertain today.