The solstice of summer and winter indicated to the ancient people about the preparatory measures to be up taken for the longer nights (sun was going to come up for another half year) especially to come up.
Explanation:
From the summer solstice until the winter solstice, nights get lengthier in duration and ancient people feared that it may someday overtake the whole of 24 hours of time. In accordance with that belief, they prepare for the hardship of winter to be faced and prayed to God against the fearful belief.
With the winter solstice coming over, they thanked God for the relief against their ghastly belief which has later turned up to be celebrated as the Christmas and birth of the deity.
