The following is an excerpt taken from page 38 of Heart Aflame: Daily Readings from Calvin in the Psalms.
Day 187 » JULY 5 » Psalm 81:1-3
Sing for joy to God our strength. This psalm, it is probable, was appointed to be sung on the festival days on which the Jews kept their solemn assemblies. In the exordium, there is set forth the order of worship which God had enjoined. They were not to stand deaf and dumb at the tabernacle; for the service of God does not consist in indolence, nor in cold and empty ceremonies; but they were, by such exercises as are here prescribed, to cherish among themselves the unity of faith; to make an open profession of their piety; to stir up themselves to continual progress therein; to endeavour to join, with one accord, in praising God; and, in short, to continue stedfast in the sacred covenant by which God had adopted them to himself.
Such having been the use of festival days under the law, we may conclude, that whenever true believers assemble together at the present day, the end which they ought to have in view is to employ themselves in the exercises of religion—to call to their remembrance the benefits which they have received from God—to make progress in the knowledge of his word—and to testify the oneness of their faith. Men only mock God by presenting to him vain and unprofitable ceremonies, unless the doctrine of faith go before, stirring them up to call upon God; and unless, also, the remembrance of his benefits furnish matter of praise. Yes, rather it is profanation of his name, when people quench the light of divine truth, and satisfy themselves with performing mere outward service. Accordingly, the faithful are here not only enjoined to come together to the tabernacle, but are also taught the end for which they are to assemble there, which is, that the free and gracious covenant which God has made with them may be brought anew to their remembrance, for increasing their faith and piety, that thus the benefits which they have received from him may be celebrated, and their hearts thereby moved to thanksgiving.
Excerpt taken from page 187 of Heart Aflame: Daily Readings from Calvin in the Psalms by John Calvin, copyright 1999, P&R Publishing.