I love the Trinity. It’s not just that I love the biblical and theological construction of it, which distinguishes Christianity from all other religions. It’s not just that I love the fact that Christians for millennia have used the doctrine as an organizing principle, such as in the Apostles’ Creed or John Calvin’s Institutes of the Christian Religion. I mean that I love the God who is triune. Because He is triune, I am sure of my salvation. Apart from a triune God, there can be no salvation, and neither can there be assurance. Let me illustrate from Romans 8.
Thomas Jacomb once described this chapter as “the grand charter of believers.” It is, in American political terms, our Bill of Rights, expressing all that is ours as believers in Jesus Christ. For this reason, Jacomb also called it “the chapter of chapters” in all the Scriptures. This charter begins with no condemnation (v. 1), what is called justification, and ends with no separation (v. 39), what is called glorification. In between, Paul explores the grand theme of the assurance of our faith.
Paul says that our assurance is the result of our triune God’s work for us. First, our assurance is rooted in the love of the Father for us: “For God [meaning the Father] has done what the law, weakened by the flesh, could not do. By sending his own Son in the likeness of sinful flesh and for sin, he condemned sin in the flesh” (v. 3). According to other passages, that “sending” is an act of the Father’s love. Earlier Paul says it like this: “God shows his love for us in that while we were still sinners, Christ died for us” (5:8).
Second, our certainty is based on the work of Jesus Christ in our behalf. There is “no condemnation” for us in Christ because the eternal Son of the Father came “in the likeness of sinful flesh”—what we call the incarnation. Why? “For sin,” that is, as a sin offering in which “he condemned sin in the flesh” on the cross.
Third, our confidence is experienced in the Holy Spirit’s work in our lives. Note the prominence of the Holy Spirit in verses 1–17. Paul speaks of the Spirit five more times in verses 23–27, but in the first seventeen verses alone he speaks of the Holy Spirit fourteen times (I take verse 10 to be speaking of our spirits in contrast to our bodies). It is He who “set you free . . . from the law of sin and death” (v. 2), who “dwells in you” (vv. 9, 11), by whom “you put to death the deeds of the body” (v. 13), who leads us (v. 14), “by whom we cry, ‘Abba! Father!’” (v. 15), who “bears witness with our spirit that we are children of God” (v. 16), and through whom God will “give life to your mortal bodies” on the last day (v. 11).
Why do I love the Trinity? Because each of the persons does a work to assure me of eternal life.