After his conversion, Paul retains his monotheism: indeed, there is only one God. But he now understands God’s unity as making room for the place of Jesus Christ as the “form” or “image” of God, or as God’s “Son.” Moreover, the actions that are attributed to God are ascribed to Christ or to the Spirit. The divine nature of both Christ and the Spirit naturally gives rise to reflections about the unity of God. Paul uses “Trinitarian formulae” involving God, the Lord Jesus Christ, and the Holy Spirit (1 Cor 12:3-7; 2 Cor 13:13; Eph 1:3-14).
Christian convictions maintain the divine nature of both Christ and the Holy Spirit, but without falling into postulating three gods. Paul was able to accommodate the risen Lord and the Spirit of Jesus into his picture of the one God of his Jewish faith. Paul does not give us a conceptual framework of the Trinity, leading to speculations about the essence of God. But he lays foundations for the later development of the doctrine of the Trinity.
