Reformed took great caution with the Regulative Principle of Worship (RPW). They only applied it to worship. Those areas that God had authoritatively addressed, all other areas of life were considered adiaphora (Greek: indifferent things). If the RPW controlled all areas, life would get difficult to resemble Phariseeism against our freedom found in Christ. Freedom, nevertheless, is controlled by God’s holy rule. All other areas of life are “ordered by the light of nature, and Christian prudence, according to the general rules of the Word.” General rules of Scripture influence private Christian piety. The Christian life is one of wisdom; the RPW only reigns in corporate worship.
What about the things in worship that are unique to a certain culture or time? There are objects in worship that seem neutral with no biblical evidence for or against like amplification. Can the church use amplification when doing so is not commanded in Scripture? Should the church worship in a house or out in a field? These are a few issues in worship not clarified in Scripture. The question is begged, “How can the church actually follow the RPW, when there are so many things found in worship not found in Scripture” and “ Should worship rid all 21st amenities to only resemble the culture and time of the 1st C.E.?” The distinction between circumstances and essences has the answer, Westminster Confession 1.6:
There are some circumstances about the worship of God, and government of the church, common to human actions and societies, which are to be ordered by the light of nature and Christian prudence, according to the general rules of the Word, which are always to be obeyed.
Reformed Christians agree that not everything connected with worship is worship. For instance the shape of buildings, the length of service, sitting and other non-religious activities have no religious significance. These are circumstances; Dr. Clark notes that anything that culture or wisdom can potentially change without affecting worship is a circumstance. Some things found in worship are just natural without any moral cultic overtones. Some things, Dr. Clark explains, are physical circumstances that aid worship, which occur alongside other civil and religious actions done by men and are not part of worship. They do not contribute moral goodness or badness to the agent in performance. Some physical circumstances, however, become moral because God sanctifies it. For example, the seventh day of the week became the Lord’s Day because he sanctified. Elements are those things that God has given spiritual significance to like prayer and the reading of Scripture. Circumstances are physical man-made things that surround worship like time or place. The RPW does allow practices as amplification to aid worship as long as the church realizes that these are only physical circumstances that could be taken away without affecting biblical worship. A pastor could remove the microphone and remain biblical, however, for example he could not remove the sermon and remain biblical. The church, therefore, may employ 21st amenities (i.e. microphone), while recognizing them as mere circumstances that help and are not worship.
 Clark, “Recovering the Reformed Confession,” 230.