Psalm singing is designed by God to provide for every expression in humanity's experience of God. Calvin said that God gave us an anatomy of the soul in the Psalter. This means that every expression of religious thought and feeling is found within the Psalter. There is truly a psalm for every human experience, thus showing the divinity in this inspired hymnal.
The lessons and encouragements which we obtain from other parts of the Old Testament are frequently drawn indirectly by a process of inference, for which we are not always in the right frame of mind and the proper spiritual mood. But the in Psalms, whatever our mood, whether we are exultant or downcast, vigorous or weary, penitent or believing, we can always find our hearts mirrored there. It needs no process of reasoning to make their sentiments our own. Here the language of the Bible comes to meet the very thoughts of our hearts before these can even clothe themselves in language and we recognize that we could not have expressed them better than the Spirit has here expressed them for us. At first sight, this may easily seem strange to us when we remember that the the psalmists lived under the conditions of a typical and preparatory dispensation; that on many points they saw through a glass darkly, whereas we, who live in the full light of the complete gospel, see face to face. But for the very reason that the Psalms reflect that experimental religion of the heart, which is unvarying at all times and under all circumstances, we need not greatly wonder at this. The influx of the divine light, whether more or less strong, must always produce the identical effect of joy, hope and peace in every soul to which it comes. The well at which we drink may flow more abundantly than that at which the psalmists drank, but the experience of thirst, of drinking and of satisfaction must still be the same as it was in the time of David. -Geerhardus Vos