The opposite field of force is the realm of the Spirit, by which Paul means God’s Holy Spirit. The Spirit was the gift of the divine presence to believers (Ro. 8:15; 1 Co. 2:12; Ga. 3:2), an eschatological deposit in view of the things to come at Christ’s return (Ro. 8:23; 2 Co. 1:22; 5:5; Ep. 1:13-14). It was not merely phenomenological, producing periodic ecstasy, but functional, serving as a working dynamic in the daily lives of believers (Ro. 8:1-2, 5, 9, 13, 26-27; Ga. 5:22-25; Ep. 3:16-17). The work of the Holy Spirit was relational, which is what Paul intends by his use of the verb “to dwell” or “to live” (Ro. 8:9, 11; 1 Co. 3:16; 6:19; 2 Co. 6:16; Ep. 3:17; 2 Ti. 1:14). Such language is not intended to be spatial, as though the Spirit were a gas. Rather, in keeping with his Hebrew tradition, Paul uses concrete expressions to describe abstract realities.
For Paul, a spiritual person is one who cooperates with the dynamic inward work of the Spirit to produce maturity and godliness (1 Co. 2:14-15; 14:37-38; Ga. 5:22-23; 6:1). In fact, it is to the point that Paul can say that the Corinthians did not lack any spiritual gift (1 Co. 1:7) but at the same time describe them as worldly (1 Co. 3:1, 3). Spiritual phenomena did not equal spiritual maturity!
The polarity between flesh and Spirit—between weakness and power—becomes a daily challenge to Christians. To live “after the flesh” is to live in weakness and the susceptibility toward sin (Ro. 7:5, 18-20; 8:4-9). The appetites of the flesh are markedly different than the desires of the Spirit. The Christian, who both lives in the flesh but who is indwelled by the Spirit, cannot satisfy the desires of both (Ga. 5:17). One or the other must have ascendancy. The difference between being “in the flesh” and “in the Spirit” is not the difference between a higher nature and a lower nature, but rather, the difference between the self, in its weakness, and Christ, in his strength. It is the inadequacy of the creature as opposed to the complete adequacy of the Lord. The Spirit is the power-sphere of the new creation and the new age, while the flesh is the power-sphere of the old creation and the old age. Paul’s language of dynamis (= power) in this regard refers to being enabled by God to live above the weakness of the flesh by being filled with hope (Ro. 15:13; Ep. 1:18-19), wisdom (1 Co. 1:24), saving faith (1 Co. 1:17-18; 2:4-5), godliness (1 Co. 4:19-20), endurance (2 Co. 4:7-10; 12:9-10; 13:4; Col. 1:11) and love (Ep. 3:14-21).
Out of this tension between flesh and Spirit Paul offers his ethic of freedom. Christ has freed the believer from the power-sphere of sin that uses the weakness of the flesh as its tool (Ro. 8:2). He challenges the believer to fully live out this freedom (Ro.8:3-4; Ga. 5:13). Human volition plays a critical role in whether the believer exercises this freedom in order to rise above sin through Christ’s empowerment or falls back into fleshly living through the inadequacy of self (Ro. 8:6-8; 1 Co. 3:1-4; 2 Co. 10:4). True spirituality, of course, is not simply a matter of will power, but rather, a dependence on Christ’s power that gives freedom. Will power alone is only another expression of the flesh (Ro. 7:18b-20).