Walter Chantry on the Regulative Principle, as found in 2 Samuel 6:

   God Regulates His Worship

   David had planned and prepared thoroughly for the worship of God on that day. Now one was dead and thirty thousand men were stunned. God was angry with them, and they were angry with God. A beautiful plan had gone seriously wrong. This is a stern lesson for a generation like our own whose people think that they can constantly reinvent worship! It appears that there is never even a question within many as to whether God will be pleased with their own original designs to approach him. All of us need to take note that noble intentions, creativity, and sincerity are not sufficient factors in determining what worship is acceptable to the Lord of hosts, who is enthroned on the cherubim!
   God is jealous about the way he is worshipped (Exod. 20:4-6, the second of the Ten Commandments). As the Westminster Confession of Faith comments on this and other Scriptures:

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 . . . any other way not prescribed in the holy Scripture (XXI:1).

   It is the Lord’s prerogative to dictate how he may be worshipped. He condescends to allow sinners to approach him, and he carefully stipulates how that may be done. With the recent history of plagues that had fallen upon the Philistines who defiled the ark, and of fifty thousand Israelites who had been slain for ignoring well-known cautions against approaching it, one would have expected that David would have taken more care in preparing to move the ark to Jerusalem.
   The Almighty had allowed the ark to return from Philistia into Israel by its being placed on a new cart and pulled along by two milk cows (1 Sam. 6). However, this method had been devised by those of worldly mindset, men who were ignorant of God’s Word. But Jews, unto whom all the prophets and all the Word of God had come, had no excuse for worshipping as do heathen peoples. Acceptable homage to God must not arise from the imagination of a worship team, not even one led by David himself! The elements of divine services of worship must arise from the Word of God itself. It is totally unacceptable presumption to imagine that God will receive any inventions of man as ways of approaching him.
   Very specific directives had been given to Israel for transporting the ark. The ark was to be covered, not opened to public view. It was to be carried on the shoulders of Kohathites, not on a cart or a wagon. Express warnings had been given that even Kohathites must not touch the ark or they would die (Num. 4:5-13).These men were to touch only the poles slipped through rings on the ark.
   Of course we do not worship by Old Testament forms today. Roman Catholicism made the mistake of creating its worship from Old Testament precedents, with priesthood, vestments, altars, sacrifices, incense, etc. The ways in which the church is to express worship are stipulated in the New Testament. Many modern practices of Protestants are not to be found among them.

—Walter J. Chantry, David: Man of Prayer, Man of War (Edinburgh, Banner of Truth Trust, 2007), 169–171.