The main ideas from this information are:
- The church believed that Jesus is fully God and fully man, one person with two natures and two wills.
- Ebionism was a heresy that denied Jesus' divinity and arose among the Jewish population where Christianity had spread.
- The first person to encounter and argue against Ebionism was Irenaeus of Lyon in 185 AD.
- Irenaeus argued that Jesus had to be God in order for salvation to be possible.
- The denial of Jesus' divinity, known as Ebionism, remained a significant issue in Christology throughout history.
All right, so remember our creed, Jesus is the man who is God, fully God, fully man, one person, two natures, two wills. So he is the man who is God. The second major heresy to hit the church denied that Jesus was God. This is called Ebionism, and it arose out of the Jewish population where Christianity had spread. The church, of course, had always taught that Jesus is God, and in the 160s you can read some of the first Antonicine fathers, Justin Martyr and Melito of Sardis, making pretty good arguments for Jesus as deity.
So it must have been an issue at least as early as that. But the first guy to really encounter this heresy in its Ebionite form and take it on full head was Irenaeus of Lyon, writing in around 185 AD. He's actually the first one who names it as Ebionism. In arguing against Ebionism, he says that Jesus had to be God if we are to be saved. If Jesus isn't God, then we cannot be saved. And this link, this connection to our salvation, is actually going to be a major deal in Christology.
This point will be picked up several times in the future in the writings of Athanasius on through to Anselm, and that is Ebionism, the denial that Jesus is God.