"Oh come, let us sing to the Lord!" (Psalm 95:1 NKJV)
God has created us to sing. Music enables us to take our deepest thoughts and feelings and give expression to them in a way that mere words cannot do. The ability to sing is even an aspect of our being made in the image of God. God sings! "He will rejoice over you with singing" (Zeph. 3:17). What a magnificent thought: Our singing out of delight in God is a reflection of his singing out of delight in his redeemed people!
Some Presbyterian and Reformed churches use only the Psalms in their worship. They believe that those are the only songs that God has ordained for use in worship. We also sing psalms because the Bible tells us to (see Eph. 5:19; Col. 3:16; Jas. 5:13). That is why some churches have a psalter in the pews along with their regular hymnal. There are songs other than the Psalms that are used in worship in the Bible (e.g., Ex. 15; Rev. 15:3-4), and the Orthodox Presbyterian Church teaches that it is appropriate to sing hymns that possess these three characteristics:
You will note that psalms (for singing) and hymns are used at various places in the worship service. The opening hymn is designed to be a suitable response to the call to worship. Its purpose is to focus your devotion on God. The hymn following the assurance of God's pardon and promises enables you to thank God for his mercies. The hymn before the sermon frequently asks for the Holy Spirit's aid as we hear the Word of God preached. The closing hymn is chosen to send us off with confidence in the Lord's grace, and to serve him in the world.