The Sunday after Pentecost is kept as Trinity Sunday.
In a sense, every feast must be a festival of the Trinity, because the whole Trinity is at work in every moment of creation, redemption and sanctification; but Trinity Sunday provides a particular occasion to reflect on the revelation of God’s self as Trinity, immediately after the Great Fifty Days of Easter.
The numbering of the following Sundays ‘after Trinity’ continues the practice of The Book of Common Prayer.