The Trinity
Trinity is the word theologians have used to express the "threeness" of the one God, that God is one being and that he is three persons. These three persons are the Father, Son, and Spirit. Each of these persons are distinct from one another; they relate to one another. It is precisely their distinction and relationship to one another as separate persons that brings the unity of the one God.
The implication of this doctrine that sets the Christian God infinitely apart from the gods of false religion is that God, when he exists apart from anything that he has created, is in his essence a loving Father. A father is only a father if he has a son. So if the Son of God was not fully God and did not exist with God the Father eternally, the Father would not be the Father; he would depend on a thing which he created to be who he is most essentially, viz., the Father, and this ruins his self-sufficiency.
Likewise, if the Father and Son ever existed apart from the Holy Spirit of love, some standard outside of these two persons - outside of God himself - would determine their essence. In other words, they would be loving only because they conform to a standard or law of love which exists outside of their relationship. God himself would not be who he is in and of himself; he must look to and depend on something that exists outside of himself to be God. Once again, this ruins his self-sufficiency.
But the standard or law which declares that the relationship between Father and Son is holy, loving, and good is God himself, yet he is a person distinct from the two; he is the Holy Spirit of Love. So God is completely self-sufficient in the relationship of Father, Son, and Spirit. He is a loving Father in his very essence as he exists in and of himself apart from what he has created, apart from anything that exists outside of himself. There was a time, in fact, when he did exist apart from everything else, and Christ declares that then the Father loved him (John 17:24).
In this way Jesus is the Truth. The Truth is that God is a loving Father. Jesus is the Truth because he is the Beloved Son. When Jesus is revealed, the world sees that God indeed has a Son and that this Son is loved by the Father. The Gospel writers make this central to the revelation of Jesus: "This is my Beloved Son; listen to him."
Jesus is what is true about this universe, because Jesus is what is true about God; God is the fountain from which reality proceeds; he is the Creator; he is the loving Father from whom all things good and beautiful shine forth (James 1:17).
What is real about life is therefore a person, namely, the Eternal Son of God. Jesus is the Truth. Truth is a Person. Knowing Jesus is knowing what is true and real about life, because knowing Jesus is knowing that God is a loving Father; and this is the essence of God himself.
Two types of knowing should be distinguished. A chemist, philosopher, or historian may know a vast amount of facts about this universe, but if he does not know Jesus he does not know anything about reality. He is on the outside looking in. In this way God has turned the wisdom of the world on its head. The most simple-minded person who does know and love Jesus (to be greatly distinguished from the discipline and science of theology) is infinitely more wise than Socrates.
The one type of knowing is only a model of the other kind. In other words, when a scientist learns a fact about the universe, that action is an image, a little picture of Trinitarian knowing, of relational knowing. When a scientist conducts an experiment and discovers a thing that is "true" about the universe - some rule or law - that is like a little dramatization of the human being who is filled with the power of the Spirit and brought into the knowledge of their Creator. This scientist experiences only an imitation of the real thing, namely, knowledge of the Creator, knowledge of the Father, Son, Spirit. Because the simple minded believer knows Jesus, he is infinitely more aware of what is real about the world than the most brilliant scientist.
Epistemology is therefore relational. Everything humanity can know calls them into relationship with their Father through the revelation of Jesus Christ his Son.
The Covenant
As God the Father is the sovereign Creator, Sustainer, and Guider of all Creation, History, and specifically what is called "salvation history," it seems to me absolutely nonsense to develop a Christian theology which does not relate to the doctrine of the Trinity. If a theologian's system cannot answer the question of how it relates to the Triune God, then they have gone about their work upside down.
I have noticed that much of the recent discussion of dispensationalism, new covenant, and covenant theology has almost nothing to do with the Triune God. I am convicted that theologians would benefit greatly if we took a few steps back in this discussion and understood how the only possibility of covenant is grounded in the Truth and Reality of the Triune God. The most obvious thing about a covenant is that it is relational, that it exists between two parties as an agreement. The Hebrew Bible reveals Trinity by teaching that God is the Father of humanity (Gen 5:1-2) and then more specifically after the fall he reveals himself as the Father of Israel (Deut 32:6; Hos 11:1; Mal 2:10). God has revealed himself as a Father. This means that his very identity and essence is wrapped up in humanity who are the sons and daughters of God. Thus, when humanity fails to live in faith and obedience and to trust their Father, his very identity and essence is blasphemed. That is why there is such strong language of wrath throughout the Hebrew Bible, especially the Pentateuch and the Prophets. When humanity has rejected their Father and looked to other means for their satisfaction and joy, they become living proclamations that God is not a loving Father, that he will not do, that humanity ought to look elsewhere for true joy and satisfaction; these are the messages that human beings proclaim when they fail to live in the covenant (as I will show) relationship between God the Father and humanity his sons and daughters.
"Hear, O heavens, and give ear, O earth; [the covenant witnesses from Deut 4:26]
for the Lord has spoken:
“Children have I reared and brought up,
but they have rebelled against me." (Is 1:2)
Israel is often rebuked as the Son of God (Deut 32:6; Hos 11:1; Mal 2:10). Their failure in the covenant is not merely a failure of walking through "do"s and "dont"s. Their failure is a relational failure involving their identity as the Son of God. In fact, the Israelites often do walk through the tasks and ceremonies of the law, and still Yahweh rebukes them strongly in their failure to live as his sons and daughters; he rebukes them because this law has become a wearisome task for them (e.g. Isaiah 1).
Further, Hosea mentions that Israel, like Adam, transgressed the covenant. This means the moral failure to live under the Mosaic law is precisely the same failure which Adam had made in the garden. Now, there are certainly several concrete covenants between specific individuals (Noah, Abraham, David, Solomon, etc.) and between the nation of Israel, but these are to be understood theologically as demonstrative of God's relationship with every human being. That is why Hosea can speak theologically and say that Adam transgressed the covenant. The covenant is this special relationship between God the Father and humanity, his sons and daughters. All humanity is called to live in his grace and goodness, yet humanity looks inward to themselves and throws away his love in their pride. All humanity is guilty of transgressing this covenant, because all humanity are created as the sons and daughters of God; that is their fundamental essence.
We speak theologically of the covenant like we speak theologically of idolatry (and New Testament writers did this too). As there are several concrete instances in "salvation history" where God makes a covenant between himself and humanity, so there are concrete instances of humanity literal bowing down and worshiping idols. But these concrete instances are demonstrative of something theologically true about humanity, viz., covenant and idolatry. The covenant between these individuals is revelatory of something pervasively true about humanity, viz., covenant; between God the Father and every human being who has ever existed there is an agreement: if they live in faith and obedience and look to their sovereign, gracious Father for their identity and worth they will experience infinite blessing; he will follow through faithfully; and if they reject the grace of the Father and build their identity and worth in their pride and selfish ambition (Gen 11:1-9) they will experience the infinite wrath of God. Covenant is pervasive. Covenant is a Trinitarian reality. It is the relationship between God and humanity which reveals God to be a Father. If humanity obeys the covenant they will experience the blessing of the infinite love of the Father; if they reject their very identity as sons and daughters, the misery of life separated from the Father will likewise reveal the reality of his goodness; the misery of those who go their own way will reveal the life that is found in the Father.
All humanity has rejected their Father. The biblical text consists of zooming in on specific groups of people who one after another fail to live as sons and daughters of God.
New Covenant
In a very real sense, the New Covenant is precisely the same as the Old Covenant. What is different about the New Covenant is that the divine Son of God has become a human being. God, instead of wiping out humanity who lives in this covenant with him, has sent his Son to become a human being and live as the Son of God. Since the meaning of the universe culminates in humanity living as the sons and daughters of God, the Incarnation of the Son of God to make this a reality must not be overlooked. If this had not happened, the meaning of the universe would be hell and utter misery.
The relationship of God and humanity is a covenant relationship between the Father and his children. The new covenant is only new in the sense that God himself has become a human being and upheld man's obligation in the covenant. This is what Jesus means when he says he did not come to abolition the law, but to fulfill it.
1 John 2:7-9 is even more precise:
"Beloved, I am writing you no new commandment, but an old commandment that you had from the beginning. The old commandment is the word that you have heard. At the same time, it is a new commandment that I am writing to you, which is true in him and in you, because the darkness is passing away and the true light is already shining."
Human beings are called into the life of God through union with Jesus. God is the infinite Love between the Father and Son. Jesus prays, "Father, I desire that they also, whom you have given me, may be with me where I am, to see my glory that you have given me because you loved me before the foundation of the world." (John 17:24)
Creation and history tell the story of sinful, treacherous humanity being brought back into the eternal joy of their Father through union with the Son; it is the story of the covenant Love of a Father for his children.