Thomas Aquinas

===Nature of the Trinity===
Thomas argued that God, while perfectly united, also is perfectly described by [[Trinity|Three Interrelated Persons]]. These three persons (Father, Son, and Holy Spirit) are constituted by their relations within the essence of God. Thomas wrote that the term "Trinity" "does not mean the relations themselves of the Persons, but rather the number of persons related to each other; and hence it is that the word in itself does not express regard to another."<ref>{{Cite book |author=Thomas Aquinas |title=Summa Theologica |chapter=The unity or plurality in God (Prima Pars, Q. 31) |chapter-url=http://www.newadvent.org/summa/1031.htm#article3 |via=newadvent.org}}</ref> The Father generates the Son (or the Word) by the relation of self-awareness. This eternal generation then produces an eternal Spirit "who enjoys the divine nature as the Love of God, the Love of the Father for the Word."

This Trinity exists independently from the world. It transcends the created world, but the Trinity also decided to give grace to human beings. This takes place through the [[Incarnation (Christianity)|Incarnation]] of the Word in the person of [[Jesus Christ]] and through the indwelling of the [[Holy Spirit in Christianity|Holy Spirit]] within those who have experienced [[salvation]] by God; according to Aidan Nichols.{{sfn|Nichols|2002|pp=173–174}}