2 In order to solve as easily as possible this most difficult problem, we must first master the knowledge which the Divine Scriptures give of Father and of Son, that so we may speak with more precision, as dealing with familiar and accustomed matters. The eternity of the Father, as we concluded after full discussion in the last Book, transcends space, and time, and appearance, and all the forms of human thought. He is without and within all things, He contains all and can be contained by none, is incapable of change by increase or diminution, invisible, incomprehensible, full, perfect, eternal, not deriving anything that He has from another, but, if ought be derived from Him, still complete and self-sufficing.
Source: On the Trinity (New Advent)