Speaking of the 10 Commandments:
The Lord, in delivering a perfect rule of righteousness, has reduced it in all its parts to his mere will, and in this way has shown that there ais nothing more acceptable to him than obedience. There is the more necessity for attending to this, because the human mind, in its wantonness, is ever and anon inventing different modes of worship as a means of gaining his favour. This irreligious affectation of religion being innate in the human mind, has betrayed itself in every age, and is still doing so, men always longing to devise some method of procuring righteousness without any sanction from the Word of God... We are certainly under the same obligations as they were; for there cannot be a doubt that the claim of absolute perfection which God made for his Law is perpetually in force. Not contented with it, however, we labour prodigiously in feigning and coining an endless variety of good works, one after another. The best cure for this vice would be a constant and deeply-seated conviction that the Law was given from heaven to teach us a perfect righteousness; that the only righteousness so taught is that which the divine will expressly enjoins; and that it is, therefore, vain to attempt, by new forms of worship, to gain the favour of God, whose true worship consists in obedience alone; scribed by the Law of God, is an intolerable violation of true and divine righteousness. [Calvin, Institutes, II.viii.5]
His emphasis is clear; true righteousness is about obeying the will of God. Obedience to His divine commands is what is pleasing to Him. Instead, we seek to invent ways to please Him all the time rather than approaching Him in a way that He has instituted. We think God will be pleased when we do X, because we do it with a sincere, authentic heart. Calvin argues that we ought to seek obedience rather than invent a new way to seek God's favour.
When we apply this to corporate worship, we find a great divide occur at the time of the Reformation with two principles of worship, the Regulative Principle of Worship (expressed below in the Westminster Confession of Faith) and the Normative Principle of Worship (below, from the 39 Articles). See if you can guess which one Calvin would support.
A) The light of nature showeth that there is a God, who hath lordship and sovereignty over all; is good, and doeth good unto all; and is therefore to be feared, loved, praised, called upon, trusted in, and served with all the hearth, and with all the soul, and with all the might. But the acceptable way of worshipping the true God is instituted by himself, and so limited by his own revealed will, that he may not be worshipped according to the imaginations and devices of men, or the suggestions of Satan, under any visible representation or any other way not prescribed in the holy Scripture.
B) The Church hath power to decree rites or ceremonies and authority in controversies of faith; and yet it is not lawful for the Church to ordain anything contrary to God's word written, neither may it so expound one place of Scripture, that it be repugnant to another. Wherefore, although the Church be a witness and a keeper of Holy Writ: yet, as it ought not to decree anything against the same, so besides the same ought it not to enforce anything to be believed for necessity of salvation.
