The happy land of the Trinity at last! All that hard work of wrestling with difficult objections and demanding texts was so that we could get somewhere. We undertook the long journey of studying the Trinity in order to arrive at the lovely destination of delighting in the Trinity. God’s triunity is not just a doctrine to be defended, but a reality to be enjoyed.
What does it look like to enjoy the Trinity? The question deserves a series of its own. For this article, one example will have to suffice: let’s enjoy how God’s triunity helps us feel secure.
A child develops best in a secure environment in which Mom and Dad are lovingly committed both to the child and to each other. It is hugely important for children to feel secure. If that’s true in the social and physical realm, it’s true in the spiritual. As God’s children, we need a strong sense of security in our relationship with God if we are to grow and flourish. And nothing spells “safe environment” like a robust theology of the Trinity.
In the opening of one of his letters, Paul composes a rhapsody that swells with joy while striking strong trinitarian chords (Eph 1:3-14). Paul leads us in uninhibited praise of God as he turns to focus on the work of the Father (vv3-6), the Son (vv7-10) and of the Holy Spirit (vv11-14). And within this trinitarian structure, believers begin to celebrate a sense of security in God.
Listen to the final movement of Paul’s praise. Here the dominant blessing on display is that we have “obtained an inheritance” (v11). Not content with rescuing us from danger, God has provided for our eternal flourishing by laying up for us an inheritance. And one of the things He wants us to enjoy right now about this inheritance is how secure it is. So many stories, historical and fictional, turn on someone losing their inheritance, but not our story, because our inheritance is as secure as the Trinity.
Secure As the Son
It’s secure, first, because we have obtained it “in him,” that is, in Christ (vv11,13). We became heirs of God’s inheritance by virtue of our union with Christ. It’s important to remember that Christ Himself is the heir, “the heir of all things” (Heb 1:2; cf. Mar 12:7). Because Jesus is God’s Son, He stands to inherit all that God possesses, which is to say, everything. As God’s children, we too are heirs, “heirs of God and fellow heirs with Christ” (Rom 8:17). And because we have the inheritance in Christ, God would have to disinherit His own Son before He could disinherit us. Our inheritance is as secure as the Son.
Secure As the Father
But God wants us to know that our inheritance is doubly secure, so He has Paul inform us that we got in on this inheritance by being “predestined according to the purpose of him who works all things according to the counsel of his will” (Eph 1:11). What does predestination have to do with this? Well, our Father lovingly “predestined us for adoption to himself as sons” (v5), and in ancient culture, “the primary connection between … adoption and the son(s) was inheritance.” A Roman head of family would adopt a son so that the son could take over the estate. Because God has predestined us – female believers included – for adoption as sons, we have obtained an inheritance.
And Paul wants to draw our attention to who exactly this Father is who bequeathed to us His vast estates. He’s the one who – get this – “works all things according to the purpose of his will” (v11). Do you see that? There’s no chance of the believer missing out. The God who controls all things, upholds all things and works all things, the God whose plans are never frustrated, is the God who predestined you to be His son and heir. It’s so certain that Paul can put it in the past tense: we have obtained an inheritance. In other words, the only way we could lose our inheritance is if God the Father lost control.
Secure As the Spirit
Our inheritance isn’t just doubly secure; it’s triply secure. The moment we heard the gospel and believed in Christ, we “were sealed with the promised Holy Spirit, who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory” (vv13-14).
The Holy Spirit is the seal, the mark God has put on us to show that we belong to Him. The Spirit is also the guarantee of our inheritance. Both terms signify security. To have received the Spirit means that you are going to receive the fullness of God’s inheritance.
Our inheritance, our final salvation, is as strong as the Trinity. Everything else in life can slip through our fingers in an instant, but our inheritance of resurrection life in the new heavens and the new earth is utterly secure. Before a Christian can lose her inheritance, God the Son would have to lose His inheritance, God the Father would have to lose control, and God the Holy Spirit would have to lose His place. The land of the Trinity is a happy place indeed!
 Of course, God’s grace is not limited. He can and does intervene in un-ideal family situations.
 Bible quotations in this article are from the ESV.
 It’s possible that Paul has primarily Jewish believers in mind in 1:11-12, and then Gentile believers in 1:13-14. But even so, his emphasis is on the fact that the things he is writing are just as true for Gentile believers as they are for Jewish Christians.
 S.M. Baugh, Ephesians: Evangelical Exegetical Commentary (Bellingham, WA: Lexham Press, 2015), 85.
 Fred Sanders, The Deep Things of God: How the Trinity Changes Everything (Wheaton, IL: Crossway, 2010), 187-92, argues that the doctrine of assurance finds its home in the doctrine of the Trinity.