Complex sentence: The Norsemen loved Eastre so much that they where not willing to surrender her holiday, by the same name, when they were christianized; therefore, her representing rebirth was associated with the rebirth of Christ, and the holiday of Easter was born.
Split into simpler sentences: The Norsemen loved Eastre so much that they where not willing to surrender her holiday, by the same name, when they were christianized. Therefore, her representing rebirth was associated with the rebirth of Christ; and the Holiday of Easter was born.