“…only two years lie between the appearance of the commentary on the Psalms (1557) and the publication of the last Latin edition of the Institutes (1559). Given certain passages which are duplicated nearly verbatim in both works, it is noticeable that Calvin worked on both books simultaneously. In light of the distinction in genre and reading audience as well as the correspondence in content, I would like to define the commentary on the Psalms as a pastoral variation of the Institutes. In his commentary in particular Calvin applies himself to the main themes of the Institutes and gives them form so that they are directly applicable to the practice of living in faith. This would also explain why Calvin sometimes brings issues into consideration during his exposition which neither appear in the text of the Psalm nor seem to directly relate to it, and meanwhile Calvin makes far fewer references to contemporary events and situations than others commentators from the era do. Hence discussions of such things as the Lord’s Supper and the Trinity do not occur at all, and the matter of election scarcely occurs.”
—Herman J. Selderhuis, Calvin’s Theology of the Psalms (Baker Academic 2007) pp. 283-284.