Some people think they are "Reformed" simply because they believe in the 5 points of Calvinism. These people are Baptists (not Reformed Baptists), independents, dispensationalists, and non-confessionalists. What is the most effective answer to show them they are not?
You raise an important question. Most evangelical Christians would say that they believe in the sovereignty of God. A smaller number would have thought about this and agree that God is sovereign in salvation. They may not know the phrase "the doctrines of grace" but believe something like it, though if you start to ask they would disagree with some of the five points (often limited atonement).
The Reformed faith doesn't separate the sovereignty of God in salvation from the sovereignty of God to address all of life. What I mean is that it really comes down to the question of authority. Do we submit to a sovereign when he speaks to us about the future or church government or the sacraments? Do we want to hear what God's Word says about all areas of our lives? If God is truly sovereign, then we must yield to his authority and that means yielding to the authority of Scripture.
The Reformed faith proclaims that the Scriptures present a system of doctrine for understanding all of life. In Presbyterianism we believe that the Westminster Standards provide us with a concise and clear summary of that system of doctrine which covers what we are to believe concerning God and what duties God requires of us (Shorter Catechism, Q. 3). So, to answer your question, I would start by inviting your Baptist, independent, dispensational friends to read and study the Westminster Standards with you, looking at the proof texts and then discussing whether the Scriptures do indeed teach the very things which the Standards claim that the Bible teaches. You may not get many Baptists to agree with you and embrace the baptism of infants, but you could at least show them that what we teach about baptism is part of a larger system of truth.
You could also direct people to the many resources that are available. For instance, the Orthodox Presbyterian Church's website has a wealth of information which is downloadable. The newly posted archives of The Presbyterian Guardian as well the publications New Horizons and Ordained Servant, would have many articles you might find of interest. There is also a downloadable pamphlet What is the Reformed Faith?.
There are many books and publishers. Several good resources would be The Reformed Doctrine of Predestination by Lorraine Boettner which is a classic on a central distinctive and Back to Basics: Rediscovering the Richness of the Reformed Faith edited by David Hagopian. When Grace Comes Home: How the Doctrines of Grace Change Your Life by Terry Johnson also is worth reading.
You can go online to several publishers like P&R Publishing and Banner of Truth Trust who have wide selections of Reformed books. There are other sources for information on the Reformed faith but I would encourage you to start with the OPC's own website and make use of the free material here.
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