From Pg. 527-528 of his Systematic Theology:

VIII. SINGING OF PSALMS

Singing of Psalms in Public, Private, and secret (1 Chron 16, Ex. 15, Isa. 52:7-9, Acts 16:25, Matt 26:30, Psalm 118:15, and James 5:13). This is a moral duty. 1. We have the example of Christ, angels, and apostles for it (Matt 26:30, Job 38:6-7, Luke 2:13-14, Acts 26:25). 2. We have an express commandment of God for it, respecting the New Testament church (Psalm 47:1-6, Col. 3:16, Col. 2:16-17, Eph. 5:19, Eph. 2:14-15). 3. God's command respecting it extends to Gentiles as well as Jews (Psalm 47:1-6, Psalm 46:1-2, Psalm 117:1-2). 4. It is distinguished from, and opposed to ceremonial worship (Psalm 119:30-31). 5. It was performed before most of the Laws of Moses were given, is, and will be after they were abolished (Ex. 15:1-22, Isa. 26:19, Rev. 14:3, Rev. 5:9, Rev 15:3-4, and Rev.19:1-2). We ought to sing psalms, 1. With understanding (Psalm 47:7, 1 Cor 14:15) 2. Under the influence of the Holy Ghost and with our own spirit fixed (1 Cor 14:15). 3. To the Lord (Col. 3:16, Eph 5:19) 4. With inward joy (James 5:13, Luke 1:47) 5. In the name of Christ (Col. 3:16-17, 1 Pet 2:5,9). 6. With affections suited to the psalms (Psalm 45:1, Psalm 108:1).