“The Old Testament prophets are frequently called seers, the men who saw. Every true Christian is a seer. He has seen the invisible, and heard things not written down in any of the philosophies of men. He has become acquainted in some measure with God, and there are great thoughts surging through his mind, and tidal waves of religious emotion swelling within him. He must speak the praises of his Lord. But he is there met by a difficulty. His words fail him. His words cannot put into expression all, or the half, of what is in his heart to say to God. His thoughts are too big for utterance. He is conscious of the need of divine aid to speak in sufficient and right terms the great themes of his worship. It is then that he turns with deepest satisfaction to the songs which the Spirit of God has written for the people of God as the expression of their devotion to Him. There the great things of God are unfolded as only the divine penman can unfold them, and there the petitions which we need to offer, and are allowed to offer, to God with assurance of being heard are framed for us.”
“while the composing of Psalms is a prophetic function, the singing of them in worship is a priestly function, an offering, the offering of praise to God, the fruit of our lips giving thanks to His name (Hebrews 13:15). The scripture, ‘Ye are an holy priesthood… to offer up spiritual sacrifices (1 Peter 2:5), constitutes every saint a priest and clearly under the law of priesthood… But all are not prophets, for He only gave “some to be prophets.” [ed. a reference to Ephesians 4:11]
“[ed. noting one of the evil fruits of singing uninspired material he argues] “It leads to confounding poetic genius and fervor with divine inspiration, to the great disparagement of the latter. It is no uncommon thing to be told that the writers of modern hymns are just as inspired as David was [or as he notes earlier simply ‘inspired’]. Is it any wonder that so many people are off on the subject of inspiration? This is not good fruit.”
“The deeper fundamental character of the Psalter consists in this that it voices the subjective response to the objective doings of God for and among his people. Subjective responsiveness is the specific quality of these songs. As prophecy is objective – being the address of Jehovah to Israel in word and act – so the Psalter is subjective, being the answer of Israel to that divine speech.”
“just as we in the consciousness of the fulfilment of prophecy, make our faith reach back into the Old Testament, so the Old Testament, by means of prophecy, prophecy, in advance lays its hand upon us: we are sons of the prophets and of the diatheke God made with Abraham. But this is a purely objective bond; it is the bond between a program and its execution; it does not directly enable us to feel our oneness with the Old Covenant people of God. No sooner, however, do we pass out from the region of prophecy into that of psalmody, than we come into touch with something that is internally akin to us, a preformation of our own living religious embrace of the realities of redemption. This must be so all the more, because our whole New Testament life and heritage was, from the Old Testament point of view, an eschatological thing. Here, therefore, we find ourselves and them occupied with identical fact; what they eschatologically contemplated we retrospectively enjoy, and the religious apprehension of it, while formally different, is in essence the same. In the eschatology of the Psalms we may trace the embryonic organism of our own full-grown state. We are enabled to see how our faith was made in secret and curiously wrought, when our substance was as yet imperfect and our members continually fashioned before the eyes of God.” 
1. McMillan, W.H. “The Idea of Worship” in The Psalms in Worship (1907), Edmonton: Still
Waters Revival Books, 1992., page 15.
2. Kennedy, James A. “The Psalms the Divinely Authorized and Exclusive Manual of Praise” in The Psalms in Worship, page 60.
3. Ibid., page 69.
4. Vos, Geerhardus. “Eschatology of The Psalter.” Gordon Faculty Online. Gordon College. Web. 16, January, 2016.