Christians believe, as I understand it, that Jesus was the "son" of God, "son" being used figuratively to describe a human-like incarnation of the deity which was made manifest by the resurrection and other remarkable phenomena.
Don't ask me to explain the Trinity - it's a mystery to me.
To non-believers, it sounds like science fiction, but even non-believers and Doubting Thomases have no doubt that Jesus (the Latinized version of Yeshua, Joshua) was an inspired and spiritually revolutionary rabbi who has been rocking the world since he lived.
For Christmas, the Beatitudes (beginning with Matthew 5), the beginning of The Sermon on the Mount.
"And he opened his mouth and taught them, saying:
“Blessed are the poor in spirit, for theirs is the kingdom of heaven.
"Blessed are those who mourn, for they shall be comforted.
"Blessed are the meek, for they shall inherit the earth.
“Blessed are those who hunger and thirst for righteousness, for they shall be satisfied.
“Blessed are the merciful, for they shall receive mercy.
“Blessed are the pure in heart, for they shall see God.
“Blessed are the peacemakers, for they shall be called sons of God.
“Blessed are those who are persecuted for righteousness' sake, for theirs is the kingdom of heaven.
“Blessed are you when others revile you and persecute you and utter all kinds of evil against you falsely on my account.
Rejoice and be glad, for your reward is great in heaven, for so they persecuted the prophets who were before you....
"You have heard that it was said, ‘You shall love your neighbor and hate your enemy.’ But I say to you, Love your enemies and pray for those who persecute you, so that you may be sons of your Father who is in heaven. For he makes his sun rise on the evil and on the good, and sends rain on the just and on the unjust. For if you love those who love you, what reward do you have?"