Council of Nicaea, Sunday & Easter

But in vain they do worship me, teaching for doctrines the commandments of men. Matthew 15:9

"The Council of Nicaea in 325 A.D. decreed that Easter should be

observed on the first Sunday following the first full moon after the spring equinox (March 21). Easter, therefore, can fall on any Sunday between March 22 and April 25." 

Britannica