The musical instruments he mentions pertained to the time of instruction.1 Nor should we stupidly imitate a practice which was proper only for God’s old [covenant] people…. They were for use under the legal cult.2
John Calvin, From his commentary on Ps 149:2 and Ps 150:3
1. Calvin regarded the Mosaic covenant as a sort of “pedagogical tool” to lead the Israelites to Christ.
2. i.e. during the Mosaic-Davidic-prophetic epochs of redemption. For Calvin, the instruments were fulfilled by the incarnation, obedience, and death of Jesus as the high priest, temple, sacrificial lamb, and true Israel of God.