The Puritan/Presbyterian wing of the Reformation accomplished a purity in worship not seen since the apostolic church. This purity was attained by making the Scriptures of the Old and New Testaments the only infallible standard and authority in determining worship ordinances. Any ordinances solely based on church tradition or man's authority were discarded. However, this purity attained by our spiritual forefathers has, with the passage of time, been cast aside. Pragmatism, tradition and human opinion are exalted in determining how God's people are to worship Him. The attitude among many in church leadership positions is to give the people what they want, rather than to submit to God's divine revelation. The purpose of this booklet is to show that God does not leave it up to man to make up his own rules regarding worship. Christians are to learn and submit to what God says in this area. The first part of this booklet discusses the "regulative principle" of Scripture and worship. God has set down in Scripture how He is to be worshipped. Man is not to add to or detract from what God says. The second part of the booklet examines the keeping of Christmas. Christmas is a good example of how many people violate this regulative principle of worship. It is celebrated almost universally, even by those who claim to adhere to the regulative principle.