Once upon a time, a long long time ago, there was a big island called Iceland. Back then, the people who lived on the island believed in many different gods and goddesses. They would pray and make offerings to these gods to keep them happy and protect them from bad things.
But one day, a man named Þorgeir Ljósvetningagoði gathered all the important people together and said, "Hey guys, we need to decide on one religion for our country. It's hard to have all these different beliefs and it causes a lot of conflict."
Some people weren't too happy about this idea because they didn't want to give up their own beliefs. But Þorgeir was very wise and knew just what to do.
He declared that Iceland would become a Christian country, and everyone had to follow this new religion. But he also said that people could keep some of their old traditions and customs as long as they didn't go against Christian beliefs.
So, the Icelanders gradually started to embrace Christianity. They built churches and monasteries and started to learn about the Bible and Jesus. But they also didn't forget about their old ways of doing things. They continued to celebrate their old holidays like the winter solstice and the summer solstice, but now they did it with a Christian twist.
And that's how Iceland became a Christian country, with a mix of old and new traditions.