The Trinity is a difficult concept to understand let alone preach about, and part of the reason is because the Trinity is not specifically mentioned anywhere in the Scriptures, even though the concept of the Trinity is mentioned throughout the Bible. There is always a danger when a man-made concept is introduced into something God has created. The early church introduced the concept of the Trinity to explain how God works in our lives to restore our relationship with him.
In essence, the Trinity is the belief that God is one in essence, but distinct in person. In other words, the Father, the Son and the Holy Spirit are somehow distinct from one another, yet at the same time they are completely united in essence, will and tasks. God has a life in which all three members of the Trinity relate to each other, give to each other, and love each other.