There are some professing theonomists who reject the regulative principle of worship; they hold to the sufficiency of Scripture in matters of the state, but reject it in matters of the church. But true theonomists hold to the sufficiency of Scripture in all areas of life, not just the state. Christ is Lord of all, and therefore His law applies in matters of church no less than matters of state.
The regulative principle of worship says that we cannot add or take away from God’s commands. Thus we cannot go beyond what the Bible authorizes regarding corporate worship. We can neither do that which the Bible forbids, nor go beyond what is commanded by doing that which the Bible is silent on.
However, those who oppose the regulative principle say that in corporate worship, we are free to do whatever we want, as long as we do not do that which the Bible forbids.
But this doesn't make sense. For if God's law doesn’t dictate what man does for worship, by what standard could man decide what constitutes a “good” worship practice? God’s law is the standard for identifying something as good or bad (cf. Rom. 7:12; 16), and so to not have the law as a standard for good worship practices is to be without any standard for good worship practices.
(One might argue that there are matters of Christian liberty, such as what food we eat, Rom. 14:20; this is true [although even matters of liberty are to be for God's glory, 1 Corinthians 10:31], however, such matters of liberty do not apply to worship. See part 3.)
If God’s law didn’t command us how to positively conduct our worship, then there would be no good reason to choose any extra-biblical worship practice, since a good worship practice can't be found outside of God's law, which is the only standard for determining what is good.
Moreover, if we don’t base our worship practices positively on God’s law, then we base our worship practices on sin, since sin is lawlessness (1 John 3:4). To be lawless is to not abide by God's law; since then everything we do outside of God’s law is lawless, then extra-biblical worship practices are lawless and thereby sinful.
Even if sincere, it is not as if finite, fallen man can reliably determine on his own whether a given worship practice is acceptable to God. From our sinful perspective, unbiblical worship practices may appear righteous, when in fact they aren’t. Colossians gives an example of practices that might appear righteous on the surface:
“If with Christ you died to the elemental spirits of the world, why, as if you were still alive in the world, do you submit to regulations—“Do not handle, Do not taste, Do not touch” (referring to things that all perish as they are used)—according to human precepts and teachings? These have indeed an appearance of wisdom in promoting self-made religion and asceticism and severity to the body, but they are of no value in stopping the indulgence of the flesh.” (Colossians 2:20-23)
Indeed, the Bible teaches, “There is a way that seems right to a man, but its end is the way to death.” (Proverbs 14:12)
Thus when it comes to corporate worship and all things else, we should not look to ourselves but to Scripture and Scripture alone as a guide:
“Trust in the LORD with all your heart, and do not lean on your own understanding.” (Proverbs 3:5)