How is Easter Determined?

I'm so confused about this. Easter is not the same day every year, how is it determined which date Easter Sunday will fall on each year? Is there a method to calculate the day?
Why does the date of Easter vary by more than a month?

Easter is an annual festival observed throughout the Christian world. The date for Easter shifts every year within the Gregorian Calendar.

The Easter date is set following these rules:

1) after the Vernal (Spring) Equinox, and 2) after the Jewish Passover, and 3) with the first full moon in Spring, and 4) on a Sunday after 21 March.

It is complicated. I think people should just set a day every year, problem solved.