I believe in one God

Why Marcionism is wrong

THEOLOGYREFLECTION

6/22/20252 min read

Yesterday, during a 4-hour drive, I decided to make the most of the time by diving into a series I had been meaning to explore: Heresies on Formed. Hosted by Dr. James Prothro and Dr. Chris Mooney, this seven-episode Catholic series walks listeners through some of the most significant heresies that have plagued the early Church and reveals how these ancient errors continue to echo in the modern world.

Just to set the tone for this post—studying heresies isn't about diving into obscure theology for its own sake. It’s about growing in our understanding of who God really is (and who He isn’t), so we can live our daily lives more rooted in the truth and more confident in our faith.

With that out of the way, I'll describe some of my learnings from the series. This post will focus more on one of the earliest heresies: Marcionism.

Maybe I prefer the God from the New Testament, Jesus seems like a nice guy, but...

I remember thinking of God in the Old Testament as this angry, justice-driven, almost vindictive figure that people were afraid of—whereas the God of the New Testament felt merciful, loving, and kind, someone you could actually approach in the form of Jesus Christ. And honestly, I wouldn't be surprised if a lot of people still see it that way.

But one of the things this series helped me realize is that this kind of thinking—even if unintentional—can actually make an old heresy called Marcionism resurface. Basically, it was a heresy proposed by Marcion, the son of a bishop, from the second century that tried to split God's nature in two, almost as if there were two different gods: one of wrath and one of mercy. He zoomed in on Paul's teaching on the Mosaic Law from the Old Testament versus the grace of God in the New Testament and concluded that Paul was right and all the other apostles got it wrong.

...if God of the Old Testament is different from One in the New Testament, then Christianity doesn't matter

Here's the thing: if the God of the Old Testament was different from the One in the New, then Christianity just doesn't hold up. The Gospel would lose all its meaning. Jesus wouldn't be the fulfillment of anything—He'd just be representing some new god, totally disconnected from the story that came before Him. That's not just bad theology; it completely empties the cross of what it means for us, therefore making Christianity lose its purpose.

Reconciling the God of both the Old and New Testaments allows us to read the Bible as a unified whole—not just cherry-picking the "good stuff" from the Gospels and ignoring the rest. When we see that God is consistent throughout Scripture, we can fully appreciate the depth of His love, His justice, and His mercy from beginning to end of the salvation history.

God doesn’t change. He is both just and merciful, both in the Old and the New Testaments. The same God who delivered Israel with power and continued to walk His people through the path of salvation despite of all the violations they have done is the same God who stooped to wash His disciples' feet. His justice and mercy are not opposites—they're perfectly united in His love. The point of the Bible is that the Old Testament is fulfilled in the New, and the New Testament is hidden in the Old.