The phrase "Holy Trinity" may be defined as "the union of the Father and Son and Holy Ghost in one Godhead (Word Book Dictionary)." Heidelberg Catechism question and answer (Q&A) number twenty five (25) rightly ask "Since there is but one Divine Being why do you speak of three three persons: Father, Son, and Holy Spirit? What is "The Heidelberg Catechism (1563)?" "The Heidelberg Catechism is a Protestant confessional document taking the form of a series of questions and answers, for use in teaching Reformed Christian doctrine. It has been translated into many languages and is regarded as one of the most influential of the Reformed catechisms" as taken from http://en.wikipedia.org/wiki/Heidelberg_Catechism. The writers and editors of this responded with the following: "Because God has so revealed Himself in His Word, that these three distinct persons are the one, true, eternal God."