The Trinity, within the context of Reformed theology, is one of those things that really boggles my mind. Before really thinking about it, I never thought about what the Trinity accomplished in the person of God and why Christian theology, as a whole, necessitates it. Before going into Its impact on Reformed theology, I feel it’s important to get an understanding of it in general. Everyone knows the verse in 1 John 4:8 that says ‘God is love.’ Everyone loves to quote that verse because it sounds really nice. But, as I heard Mark Driscoll say, that statement is essentially the same thing as saying ‘God is triune.’ At first, I didn’t really follow the statement, but the more I thought about it, the more it made sense. God cannot be love if He exists as only one person. For love to exist, there needs to be multiple persons. Thus, it follows that since God is love, there is love within God meaning that there are inter-personal relationships existing within the Godhead. Now, we do know that God is one, so how can this be? The only answer that makes sense is that God is Triune. Three persons in one God. Also, to say that God is not Triune is ot say that God is incomplete within Himself. What I mean by this is that if God did not have love existing in Himself before creation (and we know that He loves His creation) it means that He created man to have a loving relationship with him since God did not love prior to the creation of man and the world. Thus, we see that for God to be contained and fulfilled and satisfied completely within Himself requires the Trinity to be true. Personally, I find this to be very interesting and a great thing to meditate on. I never would have expected so much to be said about the character of God to be communicated in a mere three words.
Now, how the Trinity acts in the Reformed tradition really blew my mind. Within Covenant theology, there is this thing called the Covenant of Redemption. This covenant is one between the three persons of the Trinity to redeem the elect from sin. The covenant, in summary, looks like this: 1.) God (the Father) chooses those He wills to save 2.) God (the Son) agrees to die for the sins of the elect and to call them and draw them to Himself and 3.) God (the Holy Spirit) seals the elect, ensuring their inheritance. Ephesians 1:3-14 describes this covenant very clearly, and it describes it as existing before time.
3 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places, 4 even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. In love 5he predestined us for adoption as sons through Jesus Christ, according to the purpose of his will, 6 to the praise of his glorious grace, with which he has blessed us in the Beloved. 7In him we have redemption through his blood, the forgiveness of our trespasses,according to the riches of his grace, 8which he lavished upon us, in all wisdom and insight 9making known to us the mystery of his will, according to his purpose, which he set forth in Christ 10as a plan for the fullness of time, to unite all things in him, things in heaven and things on earth.11In him we have obtained an inheritance, having been predestined according to the purpose of him who works all things according to the counsel of his will, 12so that we who were the first to hope in Christ might be to the praise of his glory. 13In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit, 14who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory.
In Ephesians 1:4-5, we see that God is the one choosing the elect for salvation. He choses us to be holy and blameless in his sight (this is imparted righteousness through sanctification by the Holy Spirit.). We also see that He chose us in Him “before the foundation of the world.” Also, we see that His way of bring us into communion with Him is through adopting us through Jesus Christ. And this choosing is only according to His love and His will and not by anything we have done. Verse 6 just goes on again to restate one of the ideas in verse 5 explaining that that we are blessed in Christ (the Beloved). Then, in verses 7-10, we see the roll that Christ plays in the salvific process. Through His blood, meaning through His sacrifice, we have redemption and our sins are forgiven. And this redemption is only from the riches of His grace which He has lavished upon us (the elect). And through this redemption (salvation) we can now know His will. Last, in verse 13-14, we see that the Holy Spirit seals us and guarantees our inheritance (entrance into heaven). Here, in this passage, we see that the Trinity is in perfect agreement and that each Person of It are fulfilling their part of the salvation of the elect. If God were not Triune, He would merely be a tyrant arbitrarily choosing people to go to heaven. However, with the trinity, we see that God lovingly choses people for salvation, and it is not just an arbitrary choice. It is out of the love that has existed eternally within Him.