Does Scripture support two classes of Christians? A few observations:
1) Spiritual maturity is always a goal to be achieved, not a quality that we possess (Eph 4:13; Philip 3:12-16). Maturity is a process in you, not a character trait of you. Until we are glorified in Christ’s presence, we live between two tensions expressed in this phrase: “always aspiring but never attaining.” In this life we will always be aware of our sinful tendencies and inclinations (2 Cor 11:29; 1 Tim 1:16; Jm 3:2; 1 Jn 1:8), we will occasionally falter, but regularly seek forgiveness, and gradually grow by the power of God within us. That is the biblical reality of our human condition. We are a work in progress.
2) It follows, therefore, that while it is true that every believer has been “washed” and “sanctified” (1 Cor 6:11), it is equally true that every believer is characterized by varying degrees of holiness and sinfulness. Hence, the terms “spiritual” and “carnal” apply in some measure to all of us.
3) At the expense of oversimplifying we could say that sin, for those truly born of God, is episodal not habitual (1 Jn 1:8-10; 3:9). In every case where sinful patterns persist, they are always condemned and never condoned (cf., Heb 5:12-14). Therefore, the popular designation “carnal Christian” may be true of genuine believers temporarily but not true of genuine believers indefinitely (1 Jn 2:4). If there is a group of “Christians” who are “carnal/worldly,” Scripture clearly does not support it nor see it as the “norm.” It is an aberration from biblical standards (1 Cor. 3:1-4). Although sin’s presence remains after regeneration(1 Jn 1:8), we have no excuse for being slaves to sin (Rom 6). What changes after regeneration is our relationship to sin. Before Christ we were dominated by sin, whereas after Christ we are now dominated by the Spirit (Rom 6:6-7, 14, 17-18; 8:12-14; Gal 5:22-24). We have a new master. The Spirit’s domination is not coercive, however, but graciously and lovingly subdues our wills to want to do the things that please God.
4) God performs his work of sanctification by inspiring our desires in new directions and empowering our response to his promptings. That is why it’s reasonable for Paul to admonish us to actively put to death the deeds of our flesh (Rom 8:12-14). We no longer live under the tyranny and reign of sin (Rom 6:11-14; 18), since we “have been set free from sin and have become slaves to righteousness” (Rom 6:18). Genuine freedom for the Christian is being free from the power and penalty of sin but not from its presence. The good news is that we are now free to live the life that God intends because of his Spirit in us, whereas before becoming a Christian we were slaves to our sinful natures.
Excerpted from my essay “Our Strength, His Power: Who We Are and Why It Matters“
I fear that your first paragraph indicates that spirituality is something outside the baptised Christian, when indeed it is within. Digging deep to acknowledge what is already within is the pilgrimage of every Christian. Using St Paul’s admonishments is always a difficult row to hoe – the boundaries between good and evil use of the body can never be as clear as the manner he describes in his Epistles. The language he uses is difficult, especially the word slave and its interpretation.