By following the church calendar, we commemorate the events of our salvation each year. Trinity Sunday doesn’t celebrate an event. Instead, it shows that throughout the church year we commemorate the events of our salvation in order to encounter the God of our salvation.
During Advent and at Pentecost, we come to know the Father who gives His Son and Spirit to sons of Adam. Between Advent and Ascension, we become acquainted with God the Son who was born, suffered, died, rose, and ascended. At Pentecost, we encounter the Spirit who makes us living temples.
We need the church year because our sins and spiritual impotence come from forgetfulness of who God is. We worry because we forget that our heavenly Father cares for us. We bear burdens of guilt because we forget what the Son did on the cross and in His resurrection. We are ineffective in combating sin because we forget that the Spirit wages war against the flesh.
Trinity Sunday calls us to repent of this forgetfulness. The gospel of Trinity Sunday, and of the whole church calendar, is the good news of today’s sermon text: Behold your God.