The last chapter provided an overview of how the Christian cooperates in God’s redemptive work in Christian life. Now we begin to examine specifically the central principle of Christian morality: Christian love. Within Christian life, love of a special sort is both the supreme standard and the highest good.
Love is not something secondary or incidental in God. God is love (see S.t., 1, q. 20, a. 1). The Holy Trinity is a communion of persons in one being, one common life. Because of his love and by means of it, God communicates his love to created persons and so makes them share personally in his own life. Christian love is the new nature of a Christian who is a child of God by adoption.
Christian love often is confused with other loves. Many reduce it to sentiment or benevolence. But it is quite distinct from these loves, which, even if they are virtuous, are merely human (see S.t., 1–2, q. 109, a. 3, ad 1; 2–2, q. 23, aa. 1, 4; q. 24, aa. 2, 12). Still others identify Christian love exclusively with God’s love for us. This reduction also misses the full significance of Christian love by which we are transformed inwardly and made in truth children of God, sharers in the fullness of divinity present in Jesus in bodily form.
Aspects of human nature relevant to morality were examined in chapters two through twelve, and no extended treatise on human nature itself is required here. The present chapter will instead be devoted mainly to clarifying how God’s human children really share in his life. The model on which to understand the Christian is Jesus. He shares our human nature without detriment to his divinity; we share his divine nature without detriment to our humanity. In the Christian as in Jesus, the two distinct natures, human and divine, are united without being mingled or confused in any way.
The love of God is the principle which heals sin and all its consequences, which were considered in chapter eighteen; it is the principle of the redemptive work of the Lord Jesus, which was considered in chapter twenty-two; it is the principle of all the virtues and precepts of the way of Jesus, which will be considered in chapter twenty-six; it is the principle which is nourished in us into eternal life by prayer and the sacraments, which will be considered in chapters twenty-nine through thirty-three; and it is the principle of the Church and her gospel, which will be considered in chapter thirty-five. The love of God which begins in the present life remains forever (see 1 Cor 13.13). More than anything else, this love unites our present Christian life with everlasting life. This unity will be the main subject of chapter thirty-four. Thus the present chapter is a key one.
Confusions about the make up of the Christian have often led to the supposition that something of humanity must be sacrificed for the sake of Christian life. However, the human and divine aspects of the Christian, being on diverse planes, remain distinct and uncommingled. There can be no conflict between them, and no need to limit or compromise either for the sake of the other. Hence, these grave confusions, which have contributed so much to the flourishing and power of secular humanism during the past hundred years, can be set aside definitively, and the complex but harmonious unity of the Christian and Christian life clarified, as Vatican II already begins to do (see LG 36; GS 22, 32, 38–39, 40, and 45; AA 7).
God wills that human persons share in the love which he himself is. By living faith Christians do this and are adopted children of God. This share in divine life does not replace human fulfillment in properly human goods. The relation in the Christian between the divine and human is analogous to their relation in Jesus. As in him, so in us, divine and human life are united but not commingled, distinct but not opposed.