Last week I addressed the first part of your good question, i.e. why we put so much emphasis on singing the Psalms (not exclusively, but frequently). Let’s consider the second part of your question this week, i.e. “Aren’t some of the Psalms out of place in this New Testament period?”
What most people are referring to when they ask this question is the so-called “Imprecatory Psalms”, i.e. Psalms that call down judgments on the enemies of God and His people, e.g. Psalms 35, 58, 79, 82, 83, 109, 140.
We must admit that language like this sounds almost contrary to the great Gospel statement that Jesus did not come into the world to condemn it, but to save it, cf. Jn. 3:17
How can we sing things like this in the glorious age of the good news of the Gospel?
First, let’s keep in mind that there are also “imprecations”, i.e calls for God’s judgment, in the New Testament as well as the Old. See, for example the “woes” (calls for divine judgment) in places like Matthew 23:13, 15, 16, 23, 24, 27 (where Jesus Himself is pronouncing the judgment of God), I Cor. 16:21, 22, Gal. 5:12, and lengthy portions of the book of Revelation. In places like Matthew 26:23,24, the New Testament directly refers to the imprecations of the Psalms, cf. Psalm 41:8-10. So let’s not be too quick to say that the calls for judgment in the Psalms are our of place in this Gospel age.
Second, remember that God is a God of justice as well as mercy. The Gospel is a call to all nations (and people on every level of society in every nation) to throw down the weapons of the warfare of their hearts and surrender in repentance and faith to Jesus Christ, the King of Kings, and Lord of Lords. In Him there is a refuge from the wrath of God against the sin of humankind. BUT: Outside of Christ there is the very real promise of the kinds of just judgments we read of in both the Psalms and the New Testament. On account of these things the wrath of God comes on the sons of disobedience, Colossians 3:6. The Psalms help us to preserve this all-important (and rightly very sobering) biblical teaching).
And, finally, remember that there will be a judgment of all wickedness at the last day, e.g. II Thessalonians 1:5-10. That is far too little emphasized in modern evangelical preaching (unlike the preaching of previous ages). The Psalms will not let us forget that our God is perfectly just, and a God of judgment as well as salvation. Next week we’ll look at the key to bringing these things together.