That one iota is vitally important. With it, Arianism is the danger, hence homoousios "of the same substance" is the proper term. Three Persons, one essence is key to a proper grasp of the Trinity.
Have you read the Athanasian Creed and the Nicene Creed?
Then there is the section from the WCF:
Chapter II - Of God, and of the Holy Trinity.
I. There is but one only (Deut. 6:4; 1 Cor. 8:4,6), living, and true God (1 Thess. 1:9; Jer. 10:10), who is infinite in being and perfection (Job 11:7-9; 26:14), a most pure spirit (John 4:24) invisible (1 Tim. 1:17), without body, parts (Deut. 4:15,16; John 4:24 with Luke 24:39), or passions (Acts 14:11,15); immutable (James 1:17; Mal. 3:6), immense (1 Kings 8:27; Jer. 23:23,24), eternal (Psalm 90:2; 1 Tim. 1:17), incomprehensible (Psalm 145:3), almighty (Gen. 17:1; Rev. 4:8), most wise (Rom. 16:27), most holy (Is. 6:3; Rev. 4:8), most free (Psalm 115:3), most absolute (Ex. 3:14); working all things according to the counsel of his own immutable and most righteous will (Eph. 1:11), for his own glory (Prov. 16:4; Rom. 11:36); most loving (1 John 4:8,16), gracious, merciful, long-suffering, abundant in goodness and truth, forgiving iniquity, transgression, and sin (Ex. 34:6,7); the rewarder of them that diligently seek him (Heb. 11:6); and withal, most just, and terrible in his judgments (Neh. 9:32,33), hating all sin (Psalm 5:5,6), and who will by no means clear the guilty (Nah. 1:2,3; Ex. 34:7).
II. God hath all life (John 5:26), glory (Acts 7:2), goodness (Psalm 119:68), blessedness (1 Tim. 6:15; Rom. 9:5), in and of himself; and is alone in and unto himself all-sufficient, not standing in need of any creatures which he hath made (Acts 17:24,25), nor deriving any glory from them (Job 22:2,3), but only manifesting his own glory in, by, unto, and upon them. He is the alone fountain of all being, of whom, through whom, and to whom are all things (Rom. 11:36); and hath most sovereign dominion over them, to do by them, for them, or upon them whatsoever himself pleaseth (Rev. 4:11; 1 Tim. 6:15; Dan. 4:25,35). In his sight all things are open and manifest (Heb. 4:13), his knowledge is infinite, infallible, and independent upon the creature (Rom. 11:33,34; Psalm 147:5), so as nothing is to him contingent, or uncertain (Acts 15:18; Ezek. 11:5). He is most holy in all his counsels, in all his works, and in all his commands (Psalm 145:17; Rom. 7:12). To him is due from angels and men, and every other creature, whatsoever worship, service, or obedience he is pleased to require of them (Rev. 5:12-14).
III. In the unity of the Godhead there be three persons, of one substance, power, and eternity: God the Father, God the Son, and God the Holy Ghost (1 John 5:7; Matthew 3:16,17; 28:19; 2 Cor. 13:14): the Father is of none, neither begotten, not proceeding; the Son is eternally begotten of the Father (John 1:14,18); the Holy Ghost eternally proceeding from the Father and the Son (John 15:26; Gal. 4:6).
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Would it be accurate to say that the Holy Spirit is sent out by the Son, as the Son is sent out by the Father? Or is God the Spirit eternally proceeding from both?
I think that this is making a lot more sense now. I suppose it might be accurate to say that we can never fully understand the glory of the Trinity? Either that, or maybe a fifteen year old might take a while to grasp this!
