Tertullian on the Kingdom of God

"But we do confess that a kingdom is promised to us upon the earth, although before heaven, only in another state of existence; inasmuch as it will be after the resurrection for a thousand years in the divinely-built city of Jerusalem, "let down from heaven," which the apostle also calls "our mother from above"; and, while declaring that our... citizenship... is in heaven, he predicates of it that it is really a city in heaven. This both Ezekiel had knowledge of and the Apostle John beheld." (Tertullian, "Against Marcion")

Tertullian lived in the 2nd and 3rd centuries after Christ and is credited with coining our term "Trinity". He spoke very clearly of three Persons, sharing a single Substance. He is also credited with coining the terms "Old Testament" and "New Testament".