As far as we can reach, He Who Is, and God, are the special names of His Essence; and of these especially He Who Is, not only because when He spoke to Moses in the mount, and Moses asked what His Name was, this was what He called Himself, bidding him say to the people 'I Am has sent me' (Ex. 3:14), but also because we find that this Name is the more strictly appropriate.
Gregory of NazianzusWhat is the right time [to discuss theology]? Whenever we are free from the mire and noise without, and our commanding faculty is not confused by illusory, wandering images, leading us, as it were, to mix fine script with ugly scrawling, or sweet-smelling scent with slime. We need actually 'to be still' (Ps. 46:10) in order to know God, and when we receive the opportunity, 'to judge uprightly' (Ps. 75:2) in theology.
Gregory of NazianzusGod always was, and always is, and always will be. Or rather, God always Is. For Was and Will be are fragments of our time, and of changeable nature, but He is Eternal Being. And this is the Name that He gives to Himself when giving the Oracle to Moses in the Mount. For in Himself He sums up and contains all Being, having neither beginning in the past nor end in the future; like some great Sea of Being, limitless and unbounded, transcending all conception of time and nature, only adumbrated [intimated] by the mind, and that very dimly and scantily.
Gregory of NazianzusHow is it... that the Son and Holy Spirit are not co-unoriginate with the Father, if they are co-eternal with Him? Because they are from Him, though not after Him. 'Being unoriginate' necessarily implies 'being eternal,' but 'being eternal' does not entail 'being unoriginate,' so long as the Father is referred to as origin. So because They have a cause They are not unoriginate... a cause is not necessarily prior to its effects... Because time is not involved, They are to that extent unoriginate... for the sources of time are not subject to time.
Gregory of Nazianzus