Catholics believe that Mary is the Mother of God because Jesus is God. Here's the explanation:
* Jesus is both fully God and fully human: This is a core doctrine of Christianity. Jesus wasn't just a good man, prophet, or divine being; he was God incarnate (God in human form).
* Mary is the mother of Jesus: Mary is the person who physically bore and gave birth to Jesus.
* Therefore, Mary is the Mother of God: Since Jesus is God, and Mary is the mother of Jesus, Catholics believe it is correct to call Mary the Mother of God.
The term "Mother of God" (Theotokos in Greek) affirms the divinity of Jesus. It acknowledges that the child Mary carried and birthed was not simply a human being but was God himself in human form. It's important to note that Catholics don't believe Mary is the source of God's divinity or that she existed before God. Rather, she is the mother of the human person who is also God.