“I confess we do not forbid other songs [non-Psalms]; if grave and pious, after good advice they may be received into the Church . . . [he then cites a well-known passage from Tertullian on singing privately composed songs] . . . But that which I am to prove, that scriptural psalms may be sung [he's arguing here against those who said the Psalms were too Old Covenant and legal for us to sing], and I shall, ek perissou, with advantage over and above, prove that they are fittest to be sung.” (Works 4:441–445)

This is basically what Calvin said in his “Preface to the Genevan Psalter,” summarizing Augustine, that the Psalms are the best thing to sing [not condemning, though, other songs]. Manton also gave three qualifications for singing humanly-composed hymns: 1) they must be grave and reverent, 2) they must be pious and spiritual, and 3) they must be approved by the church as a whole.

In his monumental treatise on Puritan casuistry, De Conscientia (1630), translated and printed in London in 1639 as Conscience with the Power and Cases Thereof, he dealt with a question that perplexes Reformed churches. In our insistence upon singing the Psalms of, one issue we face almost in every Psalm are the imprecations (from the Latin, imprecatio, an invoking of a curse) against our enemies. How do we sing these words when our Lord commanded us, “Love your enemies and pray for those who persecute you” (Matt. 5:44), and the apostle Paul said, “Bless those who persecute you; bless and do not curse” (Rom. 12:14).

Thankfully we can look to our forefathers for guidance.

Quest. 4. How may we sing those Psalms aright, which contain dire imprecations in them?

8. A. 1. We may upon occasion of those imprecations meditate with fear and trembling, on the terrible judgments of God against the sins of impenitent persons.

9. 2. We may thereupon profit in patience and consolation, against the temptations which are wont to [habitually] arise from the prosperity of the wicked, and affliction of the godly.

10. 3. We may also pray to God that he would hasten his revenge (not against our private enemies but) against the wicked and incurable enemies of his Church.

—Conscience with the Power and Cases Thereof, 4.19.8–10. English modernized.