Trinity emphasizes the unity of three persons in ONE GOD. The word "trinity" is a coinage from Three-in-unity to underscore the perfect,pure relationship between the personalities in the Godhead. Doctrinally, it expresses that there is only one God, one divine nature who is tri-personal and also involves the distinctions of the Father, the son and the Holy spirit. These three are joint partakers of the same divine and majesty of God. There is one only and true God but in one co-equal persons; and they are the same in substance but in subsistence.
WHAT ARE THE SIGNIFICANCE OF THE DOCTRINE OF THE HOLY SPIRIT THEN?
Note : The doctrine of the Trinity, as have been established, is pre -eminently given to the church by revelation. And while it brings before us one of the greatest mysteries or revelation and transcends finite comprehension, it is essential to the understanding of the scripture. And as we shall see , it has great values and uses. It gives us a glimpse into the wonderful but complex being of God, while at the same time it constantly proclaims the impossibility of comprehending God.
Bible reference: John 14:9: 1:14; 1 Corinthians 2:12; John 16:12-15
Kindly: 
@orisfina
May God bless you all