Jamieson, Fausset and Brown on 2 Corinthians 6:10

10. The "as" no longer is used to express the opinion of his adversaries, but the real state of him and his fellow laborers.

making many rich--Spiritually (1Co 1:5), after the example of our Lord, who "by His poverty made many rich" (2Co 8:9).

having nothing--Whatever of earthly goods we have, and these are few, we have as though we had not; as tenants removable at will, not owners (1Co 7:30).

possessing all things--The Greek implies firm possession, holding fast in possession (compare 1Co 3:21, 22). The things both of the present and of the future are, in the truest sense, the believer's in possession, for he possesses them all in Christ, his lasting possession, though the full fruition of them is reserved for the future eternity.