The following prayer of John Calvin for purity of worship is found in the profitable collection of prayers titled, Prayers of the Reformers, compiled by Clyde Manschreck and published by Muhlenberg Press in 1958 (p.60).
This too is fitting as we end the Lord’s Day in God’s house of worship.
Grant, almighty God, inasmuch as Thou hast deigned to gather us into Thy church, that we may never turn aside in the least from the purity of Thy worship. May we always regard what pleases Thee, and learn to direct our doings and our thoughts in obedience to Thy truth, and worship Thee purely both in spirit and in external forms that Thy name may be glorified.
May we retain that purity which Thou commendest to us, that we may be indeed members of Thy only-begotten Son. As Thy Son has sanctified Himself on our account, grant that we may also through His Spirit be made partakers of the same, until He at length will gather us into His heavenly kingdom, which He has obtained for us by His own blood. Amen.