This question has been directed to me several times and I think for good reason. The term “Reformed Theology” has several different meanings, and upon asking three different people, one may come away with three different answers. My goal will be to outline what is commonly meant by “Reformed Theology”.
First, it is important to note that Reformed Theology can relate to three different fields of study. Typically, Soteriology, Ecclesiology, and Eschatology are discussed. While this is generically true, the main component has been Soteriology and thus it is common to discuss “Reformed Theology” and only mention Soteriology. As such, a person can properly call themselves “Reformed” if in fact they only hold to one of the three tenets.
Having said that, let’s examine the three fields:
Soteriology – This is the Doctrine of Salvation.
The reformed view is often referred to as the “Doctrines of Grace” or “TULIP”. The acronym can be helpful for remembering the distinctions (although the terms have led to some misunderstandings). Nevertheless, here are the five key components:
Perseverance of the Saints
Ecclesiology – This is the Doctrine of the church (specifically relating to the connection with Israel).
The Reformed position is often either called “Covenant Theology” or “Replacement Theology”. In summary, this position holds that Israel is expanded to include the church and that there is not a distinction between the peoples of God. Rather, there is one people of God, namely the Church (which Includes Israel). This position does not rule out a future moving of ethnic Jews, but sees True Israel and the Church as one body. This position believes that there are only 2 Covenants (of Works and of Grace) rather than the 3 or 7 often expressed in Dispensational thought.
Eschatology – This is the doctrine of the End times.
The Reformed position has typically been amillennial. This view holds that there is no future, earthly reign of Christ for one-thousand years. Rather, it classically has held to a Spiritual millennium with a Spiritual ruling and reigning of our Lord. Furthermore, it sees the promises to Israel fulfilled in the church (thus alleviating any need for a future earthly millennium).
Now, it is so important that I will repeat myself. Not all people who would consider themselves reformed agree with all points. The prime indicator is one’s soteriology. A so-called “5-Point” Calvinist is a Reformed believer (with respect to their soteriology). After that, Ecclesiology and Eschatology often go together (in reality they are inseparably linked).
Lastly, it should be noted that those who reject Reformed Ecclesiology are often not 5-point Calvinists. Typically Dispensationalists (these folks do see a difference between Israel and the Church) have been self-professed 4-point Calvinists (Normal Geisler is an example). While this is typically the case, there is nothing necessarily in the system of though, for Dispensationalists, which forces them out of Reformed Soteriology. John MacArthur is a prime example. While holding a dispensational view, he is very much a 5-point Calvinist (I believe he adopted the Limited Atonement view around 1998).
Hopefully that has been of some help,