There are numerous instances in Scripture where the three distinct persons of the Godhead are seen working together.  In creation, for example, the creator God [Elohim (plural)] created the heavens and the earth--other Bible passages specifically state that Jesus created all things and continues to hold them together.  Still other passages attribute creation of the world and it's inhabitants to the Holy Spirit.

Likewise, consider Jesus' resurrection.  Jesus claimed he would bring himself back to life.  Other passages say it was God who brought Jesus back to life; still others say it was the Holy Spirit.

The only way to reconcile these passages is for the three persons--Father, Son, Holy Spirit--to be of one divine essence.  The three are one God, yet God the Father, Jesus the Son, and the Holy Spirit are three distinct persons.