Belief in the trinity is of extreme importance. The early church fathers fought long and hard to retain this image of God which has become core to Christian belief and practice.
Even though there is no single reference to Trinity in the Bible the way Jesus describes his relationship to the Father and the Spirit can lead us to no other conclusion.
Down through the years, people have said that belief in the Trinity is important but have gone no further with it. But trusted scholars are beginning to show us that understanding the type of relationship that exists between Father, Son and Spirit which we call parousia is important because it describes the type of relationship we are called into with God and each other.