Yes, you’re right, we do put a lot of emphasis on singing the Psalms (especially now that we have digital access to all of the Psalms - and hymns - from the Trinity Psalter Hymnal that was published by Great Commission Publications last year). There are some denominations in the Presbyterian and Reformed community of churches that only sing Psalms (and at least in the Reformed Presbyterian Church of North America they do that magnificently - singing in all four parts!). But, in the Orthodox Presbyterian Church, most of our congregations (like The Haven) sing both Psalms and hymns. I like to say that we’re not “exclusive Psalm singers”, but we are “intensive Psalm singers”.
But, “Why?” - as you ask in part one of your good question.
The first reason is that we always want to sing those things that are most faithful to the Word of God. And it’s hard to beat singing the Word of God itself! (There’s actually a revival of chanting the Word of God in worship - but that’s not on our radar screen at The Haven).
When the apostle Paul speaks about “singing in the Spirit”, cf. I Cor. 14:15, he is speaking about what was true for that time before the New Testament was completed: The Holy Spirit gave inspired songs that were to be sung in worship. These are not recorded in Scripture, but, now that the Scriptures are complete, II Timothy 3:16f., we want to always sing songs that are conformed to the Word of God. And that’s certainly true of the 150 inspired Psalms (which were the songbook - the hymnal, if you will - of the Old Testament).
And the New Testament specifically commands us to sing the Psalms. We are to “address one another in Psalms and hymns and spiritual songs…” (Ephesians 5:19f., cf. Colossians 3:16). You can make the case that these three terms, i.e Psalms, hymns, spiritual songs, are actually specific references to the types of the 150 Old Testament Psalms. Whether or not that’s the case, this is a mandate for us to sing the Psalms.
Another reason (although there are many others) is that singing the Psalms makes us sing things that many hymns avoid. In the Psalms we sing about God’s mercy and grace; but we also sing about God’s justice and judgments. We sing about forgiveness; but we also sing about how serious sin is and what it does to us, to those around us, and to our world Rightly understood (and the one who leads you in worship should help you with this as you prepare to sing), the Psalms bring out dimensions of the person and work of Jesus Christ that hymns - especially more modern ones - frequently miss. And that impoverishes both our worship and our piety.
More on that next week. But keep in mind, as you sing the Psalms, that they are first of all about Jesus and His Kingdom, cf. Luke 24:44ff. That fascinating theme will be part three in this Haven Heart to Heart series.