The Regulative Principle of Worship
We hold to the regulative principle of worship because it is biblical. God has graciously prescribed how he is to be worshiped. He also commanded that we do not add or remove any part of that worship. For a more in-depth explanation, please see here.
Restoring the Psalms in Worship
Please refer to our Standards page for helpful material in this regard. We shall only cite John Calvin here as a good starting point:
What is there now to do in worship? It is to have songs not only honest, but also holy, which will be like spurs to incite us to pray to and praise God, and to meditate upon his works in order to love, fear, honor and glorify him. Moreover, that which St. Augustine has said is true, that no one is able to sing things worthy of God except that which he has received from him. Therefore, when we have looked thoroughly, and searched here and there, we shall not find better songs nor more fitting for the purpose, than the Psalms of David, which the Holy Spirit spoke and made through him. And moreover, when we sing them, we are certain that God puts in our mouths these, as if he himself were singing in us to exalt his glory. Wherefore Chrysostom exhorts, as well as the men, the women and the little children to accustom themselves to singing them, in order that this may be a sort of meditation to associate themselves with the company of the angels.
– Preface to the Genevan Psalter by John Calvin (1543 edition)