To unpack this title, let us mull over the meaning of I John 4:7–16, which is love.
“Love” appears some 111 times in the New Testament, as a noun (ἡ ἀγάπη). As a verb (ἀγαπάω), it appears 128 times, including as “beloved” (Ἀγαπητοί). The word famously distinguishes itself from other Greek words for love, storge(affection, such as mother and child), philia (friendship: “no greater love than this…”), and eros (romantic love). Agape (or caritas) is how God loves — it is the divine nature.
7 Beloved, let us love one another, because love is from God; everyone who loves is born of God and knows God. 8 Whoever does not love does not know God, for God is love.
We are loved before we love. Such it is to be born of God, God’s child (note the verb — γεγέννηται, the same as “the Word begotten”). And it is unconditional: you cannot be a child of God if you do not love. We have seen above that the Triune God is relation, and that relation is agape. For God is love — ὅτι ὁ θεὸς ἀγάπη ἐστίν. It is what God is, not just what God does. In these two verses lie the unbridgeable gap between the divine and us. Pierre loves or does not love, but Pierre is not love. As creature, God loves Pierre, that is the divine nature. But only when Pierre loves God and God’s creation, including, of course, other humans, can he be “begotten of God”.
9 God’s love was revealed among us in this way: God sent his only Son into the world so that we might live through him. 10 In this is love, not that we loved God but that he loved us and sent his Son to be the atoning sacrifice for our sins.
God’s agape is incomparably greater than any we can muster, even when we do so through the Spirit, without whom we can do nothing. No greater sign and work in creation is this sending, this mission of the Son, the Word. Not just that “the Word became flesh and dwelt among us” (John 1:14) but for the single reason that “just as Moses lifted up the serpent in the wilderness, so must the Son of Man be lifted up, that whoever believes in him may have eternal life.” (John 3:14)
11 Beloved, since God loved us so much, we also ought to love one another. 12 No one has ever seen God; if we love one another, God lives (μένει) in us, and his love is perfected in us.
Agape love is what makes God “visible” to us, and that agape is perfected, reaches its goal, “is finished” (τετελειωμένη — Jesus’ last word on the cross in John) in us.
13 By this we know that we abide (μένομεν) in him and he in us, because he has given us of his Spirit.
It is the gift of the Spirit, beyond the original gift of human life, that allows us to live in God and God in us, to live out in this life an image of that agape. And that requires beyond such loving to witness to the origin of our new life:
14 And we have seen and do testify that the Father has sent his Son as the Savior of the world. 15 God abides in those who confess [or, avow] that Jesus is the Son of God, and they abide in God.
And now the recapitulation:
16 So we have known and believe the love that God has for us. God is love, and those who abide (μένομεν) in love abide in God, and God abides in them.
The heart of the doctrine of the Trinity is therefore this: God is Love, the effect of the divine nature which is perfectly shared by the Three (the quality known as perichoresis, or circumincession). This love is dynamic because it is Triune, and all the attributes we ascribe to God — Power, Holiness, Humility, and so on, are summed up in that Love, and are known by it. Of course, in this simplicity we apprehend that divine Reality not by intellect, but rather by Encounter with that Love in Christ, and derivatively among us. Only after experiencing, feeling, that agape can our mind begin to try to develop a theology of the Trinity: “that obscure, analogical and imperfect understanding that can at best throw some light upon the truth known from elsewhere [i.e., agape] and enables us to possess it more fully.”
That is hard. But the Trinity is simple…
 C. S, Lewis’ The Four Loves (London: Gregory Bies, 1960) has become a classic.
 One might think of the reported last words of the poet Heinrich Heine: “Gott wird mir vergeben. Es ist sein Beruf.” God will forgive me. It’s his trade.
 And I am a long way off. Agape is a decision first of all, to decide to try and love as God loves. We are in relation always: to self, others, the creation, God. Deciding to act that way is a first sketch or draft of the image of God (Gen.1:27). “Am I my brother’s keeper?” (Gen. 4:9). Yes, sisters, brothers, we are each and all “keepers” of one another. « Le visage de mon prochain est une altérité qui ouvre l’au-delà. Le Dieu du ciel est accessible sans rien perdre de sa transcendance, mais sans nier la liberté du croyant. » — Emmanuel Levinas, Difficile liberté, essais sur le judaïsme (Paris : LGF, 1963). “My neighbor’s face is an otherness that opens up the Beyond. The God of heaven is accessible without losing his transcendence, but without denying the liberty of the believer.”
 The same verb translated “lives” in vs. 11 becomes “abide” in vss.13 and 16. “Dwell” is another alternative, and the cognate “dwelling”, “abode” or “home” (μονὴν) occurs in John 14:23: “Those who love me will keep my word, and my Father will love them, and we will come to them and make our home with them.” God with us…
 The image, humble as it is, that comes to my mind is a three-bladed propeller driving a ship forward.
 Bernard Lonergan, The Triune God: Systematics, (Toronto: University of Toronto Press, 2009), p. 107.