Today we celebrate Trinity Sunday where we proclaim the mystery of our faith in the triune God: Father, Son and Holy Spirit, One-in-Three and Three-in-One. It occurs on the first Sunday after Pentecost.
Unlike other festivals in the church’s liturgical calendar, Trinity Sunday centres on a doctrine instead of a figure or an event. It celebrates the unfathomable mystery of God’s being as Holy Trinity. It is a day of adoration and praise of the one eternal, incomprehensible God.
The doctrine of the Trinity, which is not present in Scripture, does not have any explanation, but it is taught in Scripture. Belief in the Trinity and God’s three distinct forms is a matter of complete faith and trust. Trinity Sunday allows the Church to further reflect on the mystery of God after receiving the gifts of the Holy Spirit.
The Companion to the Book of Common Worship (2003) tells us this:
Trinity Sunday, in a sense, synthesises all we have celebrated over the past months which have centred on God’s mighty acts: Christmas-Epiphany celebrating God’s taking flesh and dwelling amongst us in Jesus Christ; Easter celebrating Christ’s death and resurrection for us; Pentecost celebrating God the Holy Spirit becoming our Sanctifier, Guide and Teacher. It is, therefore, a fitting transition to that part of the year when Sunday by Sunday the work of God among us is unfolded in a more general way.
God, as Father, Son and Holy Spirit is the basis of all we are and do as Christians. We are baptised in the name of the triune God and we bear that name in our being. We are of the family of the triune God and we affirm this parentage when we declare what we believe in reciting the creeds – Nicene and Athanasian. We pray to God the Father, through Jesus Christ, by the Holy Spirit. The Trinity holds central place in our faith.
The Companion to the Book of Common Worship (2003) sums it up nicely as follows:
In celebrating Trinity Sunday, remember that every Lord’s Day is consecrated to the triune God. On the first day of the week, God began creation. On the first day of the week, God raised Jesus from the grave. On the first day of the week, the Holy Spirit descended on the newly born church. Every Sunday is special. Every Sunday is a day of the Holy Trinity.