Exodus 12:1-2, “The Lord said to Moses and Aaron…This month shall mark for you the beginning of months; it shall be the first month of the year.”
Jews divide the year into lunar months, each beginning with the new moon. Passover begins on the evening of the 14th of Nissan, and thus at the full moon. in the second century in Asia Minor (Turkey) a party strove to set Easter according to the Jewish practice. However, in 198 Victor, bishop of Rome, decided that Easter should be celebrated everywhere on the Sunday which followed the spring full moon, according to the custom which was by then already predominant.
In the first century a Jewish theologian/philosopher, Philo of Alexandria, wrote that having Passover start when the moon is full shows that there is no darkness on this day, but that it is full of light, the sun shining from dawn to the evening, and the moon from the evening to the dawn.
The Christian theologian Gregory of Nyssa writing in Asia Minor in the fourth century agreed with Philo. (The moon) having welcomed the sun when he is setting, she herself does not set before she has mingled her own rays with those of the sun, so that only one light endures without any lack of continuity, through the whole cycle of day and night, with no interval of darkness. Let your whole life, then, be one sole feast and one great day.”
I find the above pleasant to think about on day with continual rain.