And in his only begotten Son, our Lord

This is it. This is what makes Christians different from both Jews and Muslims.

We believe that God exists eternally in three persons: Father, Son, and Holy Spirit. Not three gods; one God in three persons.. I don't understand it, and anyone who says he does is probably lying.

It was the Son who lived a perfect life as Jesus of Nazareth. The Son died on the cross as an atonement for our sins. He was the one who defeated death and rose again. He's our savior.

Just like the Creed says.