Worship on the Web CHRISTIAN FESTIVALS Trinity Sunday Trinity Sunday is a day when Christians think of the nature of God rather than, as with other festivals, commemorating historical events of special significance. The Trinity, or Godhead, is a way of Christians understanding the nature of God. As in chemistry where the element H2O has three forms: ice, water and steam, Christians understand God as Father, Son and Holy Spirit. Unlike the elements though, the Trinity is seen as a warm family unit, the ultimate example of loving relationship where boundaries are blurred and understanding goes far beyond words. The ancient Celtic church referred to the Trinity as 'the one in three and three in one'. The origins of Trinity Sunday The Sunday after Pentecost was chosen as Trinity Sunday, because with the coming of the Holy Spirit at Pentecost (Acts 2:1 to 2:21), all three elements of God have now come into view. Trinity Sunday is a late addition to the Christian year originating in the Western Churches in the 10th century.