What is the most important thing in Paul's theology?
When we think of Pauline theology, I think we need to focus on what is most important in Paul's theology. And the focus, I would argue, is on God and Jesus Christ. Paul's theology is God-centered and Christ-centered. We think here of Romans 11:36, speaking of God: "For from Him and through Him and to Him are all things." So, Paul's theology is focused on God, the One from whom all things come and through whom all things are accomplished. And ultimately all things are for His glory. In Pauline theology God is the center of that theology.
But God, in Pauline theology, is magnified in Jesus Christ. God's centrality is manifested in Christ. So it is not as if God and Christ are separate, but God and Christ work together in Paul's theology. We think here of 1 Corinthians 8:6, where Paul says: "Yet for us, there is one God, the Father, from whom are all things and for whom we exist." So, all things come from God and all things are for God's glory. We exist for Him. "And one Lord, Jesus Christ, through whom are all things and through whom we exist." So we see there that Paul puts God and Christ together as equally significant and central.
If we think further about Paul's theology, we can see that Christ is preeminent in his theology. We think here of Colossians. Christ is the image of God. He reflects who God is. He is the firstborn of all creation. That does not mean that He is the first creature, but He is sovereignover all creation. He is the Creator of all. All things are created by Him and for Him (Col.1:16). But if something is created by Christ, by His agency and for His glory, then Christ is magnified in the creation. He is before all things and in Him all things hold together (Col.1:17). Christ is the Head of the church (Col.1:18). So again we see His centrality. He is to be preeminent in everything (Col.1:19).
Paul is dramatically Christ-centered, isn't he? He says, in thinking about conversion: "As you receive Christ Jesus the Lord, walk in Him" (Col.2:6). Conversion is receiving Christ as Lord. In Colossians, the false teachers go astray because they do not teach according to Christ. They move their hearers and converts away from Christ. We learn that all the fullness is in Christ and you are complete in Him (Col.2:9-10). So the only way to completion – the only way to fullness, the only way to satisfaction – is in Christ. There is no other way. Christ is glorified in that the fullness of believers is realized as believers rest in Him.