Not in the flesh (ουκ εν σαρκ). Not sold under sin (Romans 7:14) any more.

But in the spirit (αλλα εν πνευματ). Probably, "in the Holy Spirit." It is not Pantheism or Buddhism that Paul here teaches, but the mystical union of the believer with Christ in the Holy Spirit.

If so be that (ειπερ). "If as is the fact" (cf. Romans 3:30).

The Spirit of Christ (πνευμα Χριστου). The same as "the Spirit of God" just before. See also Philippians 1:19; 1 Peter 1:11. Incidental argument for the Deity of Christ and probably the meaning Rev 2 Corinthians 3:18 "the Spirit of the Lord." Condition of first class, assumed as true.